Oxidation catalyst for a diesel engine exhaust

ABSTRACT

An oxidation catalyst is described for treating an exhaust gas produced by a diesel engine comprising a catalytic region and a substrate, wherein the catalytic region comprises a catalytic material comprising: bismuth (Bi), antimony (Sb) or an oxide thereof; a platinum group metal (PGM) selected from the group consisting of (i) platinum (Pt), (ii) palladium (Pd) and (iii) platinum (Pt) and palladium (Pd); and a support material, which is a refractory oxide; wherein the platinum group metal (PGM) is supported on the support material; and wherein the bismuth (Bi), antimony (Sb) or an oxide thereof is supported on the support material and/or the refractory oxide comprises the bismuth, antimony or an oxide thereof.

FIELD OF THE INVENTION

The invention relates to an oxidation catalyst and an exhaust system fortreating an exhaust gas produced by a diesel engine. The inventionfurther relates to a vehicle comprising the oxidation catalyst or theexhaust system.

BACKGROUND TO THE INVENTION

Generally, there are four classes of pollutant that are legislatedagainst by inter-governmental organisations throughout the world: carbonmonoxide (CO), unburned hydrocarbons (HCs), oxides of nitrogen (NO) andparticulate matter (PM). As emissions standards for permissible emissionof pollutants in exhaust gases from vehicular engines becomeprogressively tightened, there is a need to provide improved catalyststhat are able to meet these standards and which are cost-effective.

For diesel engines, an oxidation catalyst (often referred to as a dieseloxidation catalyst (DOC)) is typically used to treat the exhaust gasproduced by such engines. Diesel oxidation catalysts generally catalysethe oxidation of (1) carbon monoxide (CO) to carbon dioxide (CO₂), and(2) HCs to carbon dioxide (CO₂) and water (H₂O). Exhaust gastemperatures for diesel engines, particularly for light-duty dieselvehicles, are relatively low (e.g. about 400° C.) and so one challengeis to develop durable catalyst formulations with low “light-off”temperatures.

The activity of oxidation catalysts, such as DOCs, is often measured interms of its “light-off” temperature, which is the temperature at whichthe catalyst starts to perform a particular catalytic reaction orperforms that reaction to a certain level. Normally, “light-off”temperatures are given in terms of a specific level of conversion of areactant, such as conversion of carbon monoxide. Thus, a T50 temperatureis often quoted as a “light-off” temperature because it represents thelowest temperature at which a catalyst catalyses the conversion of areactant at 50% efficiency.

Exhaust systems for diesel engines may include several emissions controldevices. Each emissions control device has a specialised function and isresponsible for treating one or more classes of pollutant in the exhaustgas. The performance of an upstream emissions control device, such as anoxidation catalyst, can affect the performance of a downstream emissionscontrol device. This is because the exhaust gas from the outlet of theupstream emissions control device is passed into the inlet of thedownstream emissions control device. The interaction between eachemissions control device in the exhaust system is important to theoverall efficiency of the system.

Oxidation catalysts can also be formulated to oxidise some of the nitricoxide (NO) that is present in the exhaust gas to nitrogen dioxide (NO₂).Even though nitrogen dioxide (NO₂) is itself a pollutant, the conversionof NO into NO₂ can be beneficial. The NO₂ that is produced can be usedto regenerate particulate matter (PM) that has been trapped by, forexample, a downstream diesel particulate filter (DPF) or a downstreamcatalysed soot filter (CSF). Generally, the NO₂ generated by theoxidation catalyst increases the ratio of NO₂:NO in the exhaust gas fromthe outlet of the oxidation catalyst compared to the exhaust gas at theinlet. This increased ratio can be advantageous for exhaust systemscomprising a downstream selective catalytic reduction (SCR) catalyst ora selective catalytic reduction filter (SCRF™) catalyst. The ratio ofNO₂:NO in the exhaust gas produced directly by a diesel engine may betoo low for optimum SCR or SCRF catalyst performance.

SUMMARY OF THE INVENTION

The invention provides an oxidation catalyst for treating an exhaust gasproduced by a diesel engine comprising a catalytic region and asubstrate, wherein the catalytic region comprises a catalytic materialcomprising:

-   -   bismuth (Bi), antimony (Sb) or an oxide thereof;    -   a platinum group metal (PGM) selected from the group consisting        of (i) platinum (Pt), (ii) palladium (Pd) and (iii) platinum        (Pt) and palladium (Pd); and    -   a support material, which is a refractory oxide;        wherein the platinum group metal (PGM) is supported on the        support material, and wherein the bismuth (Bi), antimony (Sb) or        an oxide thereof is supported on the support material and/or the        refractory oxide comprises the bismuth (BD, antimony (Sb) or an        oxide thereof.

The inventors have surprisingly found that:

(a) the presence of bismuth or an oxide thereof in combination with aplatinum group metal on certain support materials provides excellentcarbon monoxide (CO) oxidation activity. Advantageously, the CO lightoff temperature for such oxidation catalysts is very low; and(b) the presence of antimony or an oxide thereof in combination with aplatinum group metal on certain support materials provides excellentcarbon monoxide (CO) and hydrocarbon (HC) oxidation activity.Advantageously, the CO and HC light off temperatures for such oxidationcatalysts are very low. Additionally, the presence of antimony (Sb) isnot detrimental to the nitric oxide (NO) oxidation activity of thecatalytic material.

The invention also relates to an exhaust system for treating an exhaustgas produced by a diesel engine. The exhaust system comprises theoxidation catalyst of the invention and optionally an emissions controldevice.

The invention further provides a vehicle. The vehicle comprises a dieselengine and either an oxidation catalyst or an exhaust system of theinvention.

The invention also relates to the use of an oxidation catalyst to treatan exhaust gas produced by a diesel engine. The oxidation catalyst is anoxidation catalyst in accordance with the invention.

Also provided by the invention is a method of treating an exhaust gasproduced by a diesel engine. The method comprises the step of passing anexhaust gas produced by a diesel engine through an exhaust systemcomprising the oxidation catalyst of the invention.

In the use and method aspects of the invention, it is preferable thatthe exhaust gas is produced by a diesel engine run on fuel, preferablydiesel fuel, comprising ≤50 ppm of sulfur, more preferably ≤15 ppm ofsulfur, such as ≤10 ppm of sulfur, and even more preferably ≤5 ppm ofsulfur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 5 are schematic representations of oxidation catalysts of theinvention. In each of the Figures, the left hand side represents aninlet end of the substrate and the right hand side represents an outletend of the substrate.

FIG. 1 shows an oxidation catalyst having a first catalytic layer (2)containing bismuth, antimony or an oxide thereof (e.g. the refractoryoxide may comprise bismuth, antimony or an oxide thereof). The firstcatalytic layer (2) is disposed on a second catalytic layer (3). Thesecond catalytic layer (3) is disposed on the substrate (1).

FIG. 2 shows an oxidation catalyst having a first catalytic zone (2)containing bismuth, antimony or an oxide thereof (e.g. the refractoryoxide may comprise bismuth, antimony or an oxide thereof). There is alsoa second catalytic zone (3) disposed on the substrate (1).

FIG. 3 shows an oxidation catalyst having a first catalytic zone (2)containing bismuth, antimony or an oxide thereof (e.g. the refractoryoxide may comprise bismuth, antimony or an oxide thereof). The firstcatalytic zone (2) is disposed or supported on a second catalytic layer(3) at or near an inlet end of the substrate (1). The second catalyticlayer (3) is disposed on the substrate (1).

FIG. 4 shows an oxidation catalyst having a first catalytic zone (2)containing bismuth, antimony or an oxide thereof (e.g. the refractoryoxide may comprise bismuth, antimony or an oxide thereof). The firstcatalytic zone (2) is disposed on both a substrate (1) and a secondcatalytic zone (3).

FIG. 5 shows an oxidation catalyst having a first catalytic layer (2)containing bismuth, antimony or an oxide thereof (e.g. the refractoryoxide may comprise bismuth, antimony or an oxide thereof). The firstcatalytic zone (2) is disposed on both a substrate (1) and a secondcatalytic zone (3).

FIG. 6 shows an oxidation catalyst having a first catalytic zone (2)containing bismuth, antimony or an oxide thereof (e.g. the refractoryoxide may comprise bismuth, antimony or an oxide thereof), and a secondcatalytic zone (3). The first catalytic zone (2) and the secondcatalytic zone (3) are disposed on a third catalytic layer (4). Thethird catalytic layer (4) is disposed on a substrate (1).

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be further described. The followingsections relate to different parts of the oxidation catalyst of theinvention and define each part in more detail. Each part or aspect ofthe oxidation catalyst (e.g. the catalytic region, the second catalyticregion, the substrate etc.) may be combined with any other part oraspect of the oxidation catalyst unless clearly indicated to thecontrary. In particular, any feature indicated as being preferred oradvantageous may be combined with any other feature or featuresindicated as being preferred or advantageous.

Catalytic Region (First)

The oxidation catalyst of the invention comprises a catalytic region. Inoxidation catalysts comprising two or more catalytic regions, thecatalytic region comprising bismuth, antimony or an oxide thereof and asupport material, which is a refractory oxide (e.g. a refractory thatmay comprise bismuth or antimony), is referred to herein as the “firstcatalytic region”.

The catalytic material may comprise, or consist essentially of, bismuthor an oxide thereof, a platinum group metal (PGM) selected from thegroup consisting of (i) platinum (Pt), (ii) palladium (Pd) and (iii)platinum (Pt) and palladium (Pd); and a support material, which is arefractory oxide.

Additionally or alternatively, the catalytic material may comprise, orconsist essentially of, antimony or an oxide thereof, a platinum groupmetal (PGM) selected from the group consisting of (i) platinum (Pt),(ii) palladium (Pd) and (iii) platinum (Pt) and palladium (Pd); and asupport material, which is a refractory oxide. The platinum group metal(PGM) and the antimony (Sb) or an oxide thereof is each supported on thesupport material

When the catalytic region comprises antimony or an oxide thereof, thenthe antimony or an oxide thereof is preferably supported on the supportmaterial, particularly the refractory oxide thereof. The refractoryoxide may also comprise antimony or an oxide thereof. Small amounts ofantimony may be impregnated into the refractory oxide as part of thepreparative method. It is preferred that the bulk of the antimony islocalised at the surface of the support material.

The oxide of antimony may be diantimony tetroxide (Sb₂O₄), antimonytrioxide (Sb₂O₃), antimony pentoxide (Sb₂O₅) and/or antimonyhexitatridecoxide (Sb₆O₁₃). Typically, the oxide of antimony is antimonytrioxide (Sb₂O₃).

The antimony or an oxide thereof is supported on the support material.More preferably, the antimony or an oxide thereof is disposed directlyonto or is directly supported by the support material. The antimony oran oxide thereof (e.g. particles of the antimony or an oxide thereof) istypically supported on the support material by being dispersed over asurface of the support material, more preferably by being dispersedover, fixed onto a surface of and/or impregnated onto or within thesupport material.

For the avoidance of doubt, when the refractory oxide comprises antimonyor an oxide thereof, the support material or the refractory oxidethereof is not antimony or an oxide thereof (i.e., the support materialor the refractory oxide thereof is not solely antimony or an oxidethereof).

When the catalytic region comprises bismuth or an oxide thereof, thenthe bismuth or an oxide thereof is preferably supported on the supportmaterial, particularly the refractory oxide thereof. More preferably,the bismuth or an oxide thereof is disposed directly onto or is directlysupported by the support material. The bismuth or an oxide thereof (e.g.particles of the bismuth or an oxide thereof) is typically supported onthe support material by being dispersed over a surface of the supportmaterial, more preferably by being dispersed over, fixed onto a surfaceof and/or impregnated within the support material.

The oxide of bismuth is typically bismuth (III) oxide (Bi₂O₃). It ispreferred that the refractory oxide comprises an oxide of bismuth,preferably bismuth (III) oxide (Bi₂O₃).

The refractory oxide may comprise bismuth or an oxide thereof.Additionally or alternatively, bismuth or an oxide thereof may besupported on the support material, particularly the refractory oxidethereof.

For the avoidance of doubt, when the refractory oxide comprises bismuthor an oxide thereof, the support material or the refractory oxidethereof is not bismuth or an oxide thereof (i.e. the support material orthe refractory oxide thereof is not solely bismuth or an oxide thereof).

Without being bound by theory, it is believed that the bismuth ispresent in the form of an oxide, which is support on the supportmaterial and/or in the support material. The bismuth oxide is able toact as a promoter for CO oxidation because it has a high oxygen ionconductivity and a high content of mobile oxide.

When the refractory oxide comprises bismuth, antimony or an oxidethereof, then the catalytic region may comprise, or consist essentiallyof, a catalytic material. The catalytic material may comprise, orconsist essentially of, a platinum group metal (PGM) and a supportmaterial, wherein the platinum group metal (PGM) is supported on thesupport material.

In general, when the refractory oxide comprise bismuth or an oxidethereof, the refractory oxide comprises an effective amount of bismuthor an oxide thereof to promote CO oxidation. The effective amount may ormay not be sufficient to inhibit the oxidation of SO₂ to SO₃. It is,however, preferred that the diesel engine is run on a low sulfurcontaining diesel fuel. When a diesel engine is run on a low sulfurcontaining diesel fuel, the effect of bismuth or an oxide thereof on theoxidation of SO₂ to SO₃ is negligible.

Typically, the support material is a particulate refractory oxide.

The bismuth or an oxide thereof is typically (i) dispersed over asurface of the particulate refractory oxide (e.g. supported on therefractory oxide) and/or (ii) contained within the bulk particulatestructure of the refractory oxide, such as described below.

The antimony or an oxide thereof is typically dispersed over a surfaceof the particulate refractory oxide (e.g. supported on the refractoryoxide). The antimony or an oxide thereof may also be contained withinthe bulk particulate structure of the refractory oxide.

The particulate refractory oxide may be impregnated with bismuth,antimony or an oxide thereof. Thus, for example, particles of a mixed orcomposite oxide of silica-alumina, particles of alumina doped withsilica may be impregnated with bismuth, antimony or an oxide thereof. Aparticulate refractory oxide may be impregnated with bismuth, antimonyor an oxide thereof using conventional techniques that are known in theart.

The particulate refractory oxide preferably comprises pores (i.e. it isporous). The bismuth, antimony or oxide thereof may be in the pores(e.g. of the particulate refractory oxide), preferably bismuth or anoxide thereof. When the particulate refractory oxide is impregnated withbismuth, antimony or an oxide thereof, then bismuth, antimony or oxidethereof will be present in the pores of the particulate refractoryoxide.

Additionally or alternatively, the refractory oxide is doped withbismuth, antimony or an oxide thereof, preferably bismuth or an oxidethereof. It is to be understood that any reference to “doped” in thiscontext refers to a material where the bulk or host lattice of therefractory oxide is substitution doped or interstitially doped with adopant. In some instances, small amounts of the dopant may be present ata surface of the refractory oxide. However, most of the dopant willgenerally be present in the body of the refractory oxide.

When the refractory oxide is doped with bismuth, antimony or an oxidethereof, it may be preferable that the refractory oxide comprisesalumina or a mixed or composite oxide of silica and alumina.

In general, bismuth or an oxide thereof may or may not be present (e.g.dispersed) on a surface of the particulate refractory oxide. It ispreferred that the bismuth or an oxide thereof is present on a surfaceof the particulate refractory oxide.

The first catalytic region typically comprises a total loading ofbismuth of 1 to 200 g ft⁻³, such as 5 to 175 g ft⁻³.

The first catalytic region typically comprises a total loading ofantimony of 1 to 500 g ft⁻³, (e.g., 1 to 200 g ft⁻³), such as 5 to 175 gft⁻³.

The loading refers to the amount of bismuth or antimony that is present,whether in an elemental form or as part of a compound, such as an oxide.It is has been found that the inclusion of large amounts of bismuth canaffect the catalytic region's oxidative activity toward hydrocarbons.

It is preferred that the first catalytic region comprises a totalloading of bismuth or antimony of 10 to 100 g ft⁻³, more preferably 25to 75 g ft⁻³.

Typically, the first catalytic region, or the refractory oxide thereof,comprises bismuth or antimony (e.g. as an element or in the form of anoxide) in an amount of 0.1 to 15.0% by weight (e.g. of the refractoryoxide), preferably 0.5 to 10.0% by weight (e.g. 0.75 to 5.0% by weight),more preferably 1.0 to 7.5% by weight. These ranges refer to the amountof bismuth or antimony in relation to the amount of the refractory oxidethat is part of the support material, whether the bismuth or antimony is(i) dispersed over a surface of the particulate refractory oxide and/or(ii) contained within the bulk particulate structure of the refractoryoxide (e.g. impregnated and/or in the pores) and/or (iii) as a dopant ofthe refractory oxide.

The combination of bismuth or an oxide thereof with a refractory oxideas defined below when used as a support material for a PGM hasunexpectedly been found to provide advantageous CO oxidation activity.

The combination of antimony or an oxide thereof with a refractory oxideas defined below when used in conjunction with a PGM has unexpectedlybeen found to provide advantageous CO and HC oxidation activity.

It is preferred that the first catalytic region comprises bismuth orantimony in an amount of 1.0 to 2.5% by weight (e.g. of the refractoryoxide), preferably 1.25 to 2.25% by weight (e.g. 1.25. to 2.0% byweight), more preferably 1.5 to 2.0% by weight (e.g. 1.5 to 1.75% byweight). The loading refers to the amount of bismuth or antimony that ispresent, whether in an elemental form or as part of a compound, such asan oxide. As mentioned above, the relative proportion of bismuth orantimony to the refractory oxide can affect the oxidative activity ofthe catalytic material toward hydrocarbons.

The first catalytic region preferably comprises bismuth or antimony inan amount of 0.25 to 1.25 mol % (e.g. relative to the molar amount ofthe refractory oxide), preferably 0.50 to 1.10 mol % (e.g. 0.50 to 1.00mol %), more preferably 0.60 to 0.90 mol % (e.g. 0.65 to 0.85 mol %).

Typically, the support material is a refractory oxide. The refractoryoxide preferably comprises alumina, silica or a mixed or composite oxideof silica and alumina. It is preferred that the refractory oxidecomprises alumina. More preferably, the refractory oxide is a mixed orcomposite oxide of silica-alumina.

When the refractory oxide is a mixed or composite oxide ofsilica-alumina, then preferably the refractory oxide comprises 0.5 to45% by weight of silica (i.e. 55 to 99.5% by weight of alumina),preferably 1 to 40% by weight of silica, more preferably 1.5 to 30% byweight of silica (e.g. 1.5 to 10% by weight of silica), particularly 2.5to 25% by weight of silica, more particularly 3.5 to 20% by weight ofsilica (e.g. 5 to 20% by weight of silica), even more preferably 4.5 to15% by weight of silica.

When the refractory oxide comprises, or consists essentially of,alumina, then the alumina may optionally be doped (e.g. with a dopant).The dopant may comprise, or consist essentially, of silicon (Si) or anoxide thereof. Alumina doped with a dopant can be prepared using methodsknown in the art or, for example, by a method described in U.S. Pat. No.5,045,519.

When the alumina is doped with a dopant comprising silicon or an oxidethereof, then preferably the alumina is doped with silica. The aluminais preferably doped with silica in a total amount of 0.5 to 45% byweight (i.e. % by weight of the alumina), preferably 1 to 40% by weight,more preferably 1.5 to 30% by weight (e.g. 1.5 to 10% by weight),particularly 2.5 to 25% by weight, more particularly 3.5 to 20% byweight (e.g. 5 to 20% by weight), even more preferably 4.5 to 15% byweight.

The support material or the refractory oxide thereof preferably does notcomprise copper, particularly copper oxide (CuO).

The catalytic material comprises a platinum group metal (PGM) disposedor supported on the support material. The PGM may be disposed directlyonto or is directly supported by the support material (e.g. there is nointervening material between the PGM and the support material).

Typically, the PGM is dispersed on the support material (e.g. particlesof the PGM are dispersed over the surface of the particulate refractoryoxide). The PGM is preferably not in the pores of the support materialand/or the support material is not impregnated with the PGM.

The platinum group metal (PGM) is selected from the group consisting of(i) platinum (Pt), (ii) palladium (Pd) and (iii) platinum (Pt) andpalladium (Pd). The platinum group metal (PGM) may be present in thecatalytic material in metallic form or an oxide thereof.

The platinum group metal (PGM) may preferably be palladium. Thecatalytic material may comprise palladium as the only platinum groupmetal (PGM) and/or the only noble metal. Surprisingly, it has been foundthat the presence of bismuth or an oxide thereof (when used incombination with a specific support material as defined herein) canprovide a catalytic material having excellent CO oxidation when thecatalytic material comprises palladium as the only PGM.

The platinum group metal (PGM) may preferably be platinum. The catalyticmaterial may comprise platinum as the only platinum group metal (PGM)and/or the only noble metal.

It has been found that advantageous oxidation activity toward carbonmonoxide (CO), particularly a low CO light off temperature (T50), can beobtained when platinum is the PGM. The CO light off temperature of acatalytic material comprising Pt as the only PGM may be lower than somecatalytic materials containing both Pt and Pd (e.g. in a weight ratio of2:1).

The catalytic material may comprise platinum and palladium (i.e. theplatinum group metal (PGM) is platinum and palladium). Both the platinumand the palladium are disposed or supported on the support material.Particles of platinum and palladium may be dispersed over a surface ofthe particulate refractory oxide.

The platinum and palladium may be in the form of an alloy, preferably abimetallic alloy. Thus, the platinum group metal (PGM) may thereforecomprise, or consist essentially of, an alloy of platinum and palladium.

When the catalytic material comprises platinum and palladium, thentypically the ratio by weight of platinum to palladium is 20:1 to 1:20(e.g. 15:1 to 1:15), preferably 10:1 to 1:10 (e.g. 7.5:1 to 1:7.5), morepreferably 5:1 to 1:5 (e.g. 3:1 to 1:3). It may be preferable that theratio by weight of platinum to palladium is a ≥1:1, particularly >1:1.

It is particularly preferred that the ratio by weight of platinum topalladium is 20:1 to 1:1 (e.g. 20:1 to 2:1, particularly 20:1 to 5:1,such as 20:1 to 7:1), more preferably 17.5:1 to 2.5:1, particularly 15:1to 5:1, and still more preferably 12.5:1 to 7.5:1.

It has been found that CO oxidation activity, particularly a low COlight off temperature (T50), can be obtained when the catalytic materialcontains both platinum and palladium, particularly in combination withbismuth, and the catalytic material is relatively platinum rich.Surprisingly, the CO oxidation activity of, for example, a catalyticmaterial comprising Pt and Pd in a weight ratio of 10:1 shows excellentCO oxidation light off activity compared to a catalytic materialcontaining Pt only or Pt:Pd in a weight ratio of 2:1. The addition of arelatively small amount of Pd also provides excellent hydrocarbon (HC)and/or nitric oxide (NO) oxidation performance. Thus, the catalyticmaterial may have a low HC light off temperature and show excellent NOconversion performance.

The catalytic material typically comprises a ratio by weight of theplatinum group metal (PGM) to bismuth (Bi) or antimony (Sb) of 10:1 to1:10 (e.g. 1:1 to 1:10), preferably 4:1 to 1:7.5 (e.g. 1:1.5 to 1:7.5),more preferably 2:1 to 1:5, particularly 1:1 to 1:4.

It is preferred that the catalytic material comprises a ratio by weightof the platinum group metal (PGM) to bismuth (Bi) or antimony (Sb) of5:1 to 1:2, more preferably 4:1 to 3:5 (e.g. 5:2 to 3:5), such as 2:1 to1:1. It has been found that the relative proportion of PGM to bismuthcan affect the oxidative activity of the catalytic material towardhydrocarbons.

When the catalytic material comprises bismuth or an oxide thereof, therefractory oxide may further comprise tin (Sn) or an oxide thereof. Theoxide of tin is typically tin (II) oxide (SnO) and/or tin dioxide(SnO₂). It is preferred that the refractory oxide comprises an oxide oftin, particularly when the PGM is platinum. When tin or an oxide thereofis included, the sintering resistance of platinum can be improved and/oran improvement in HC oxidation activity may be obtained.

The tin or an oxide thereof is typically contained within the bulkparticulate structure of the refractory oxide.

The particulate refractory oxide may be impregnated with tin or an oxidethereof. Thus, for example, particles of a mixed or composite oxide ofsilica-alumina, particles of alumina doped with silica or particlesalumina doped with tin or an oxide thereof may be impregnated with bothbismuth (or an oxide thereof) and tin (or an oxide thereof). Theparticulate refractory oxide may be impregnated with tin or an oxidethereof using conventional techniques that are known in the art.

The tin or oxide thereof is preferably in the pores (e.g. of theparticulate refractory oxide). When the particulate refractory isimpregnated with tin or an oxide thereof, then tin or oxide thereof willbe present in the pores of the particulate refractory oxide.

Typically, the refractory oxide comprises tin in an amount of 0.1 to10.0% by weight (e.g. of the refractory oxide), preferably 0.5 to 7.5%by weight (e.g. 0.75 to 5.0% by weight), more preferably 1.0 to 5.0% byweight.

The catalytic region may further comprise a hydrocarbon adsorbentmaterial. The hydrocarbon adsorbent material may be a zeolite.

It is preferred that the zeolite is a medium pore zeolite (e.g. azeolite having a maximum ring size of ten tetrahedral atoms) or a largepore zeolite (e.g. a zeolite having a maximum ring size of twelvetetrahedral atoms). It may be preferable that the zeolite is not a smallpore zeolite (e.g. a zeolite having a maximum ring size of eighttetrahedral atoms).

Examples of suitable zeolites or types of zeolite include faujasite,clinoptilolite, mordenite, silicalite, ferrierite, zeolite X, zeolite Y,ultrastable zeolite Y, AEI zeolite, ZSM-5 zeolite, ZSM-12 zeolite,ZSM-20 zeolite, ZSM-34 zeolite, CHA zeolite. SSZ-3 zeolite, SAPO-5zeolite, offretite, a beta zeolite or a copper CHA zeolite. The zeoliteis preferably ZSM-5, a beta zeolite or a Y zeolite.

When the catalytic region comprises a hydrocarbon adsorbent, the totalamount of hydrocarbon adsorbent is 0.05 to 3.00 g in⁻³, particularly0.10 to 2.00 g in⁻³, more particularly 0.2 to 1.0 g in⁻³. For example,the total amount of hydrocarbon adsorbent may be 0.8 to 1.75 g in⁻³,such as 1.0 to 1.5 g in⁻³.

In general, it is preferred that the oxidation catalyst of the inventionor the catalytic region or the catalytic material is substantially freeof gold. More preferably, the oxidation catalyst of the invention or thecatalytic region or the catalytic material does not comprise gold.

Additionally or alternatively, the catalytic region or the catalyticmaterial is substantially free of manganese. More preferably, thecatalytic region or the catalytic material does not comprise manganese.

In general, the catalytic region or the catalytic material does notcomprise clay, particularly bentonite.

The catalytic region is preferably substantially free of rhodium and/ora NO_(x) storage component comprising, or consisting essentially of, anoxide, a carbonate or a hydroxide of an alkali metal, an alkaline earthmetal and/or a rare earth metal (except for an oxide of cerium (i.e.from the oxygen storage material)). More preferably, the catalyticregion does not comprise rhodium and/or a NO_(x) storage componentcomprising, or consisting essentially of, an oxide, a carbonate or ahydroxide of an alkali metal, an alkaline earth metal and/or a rareearth metal.

The catalytic region typically has a total loading of the PGM of 5 to300 g ft⁻³. It is preferred that the catalytic region has a totalloading of the PGM of 10 to 250 g ft⁻³ (e.g. 75 to 175 g ft⁻³), morepreferably 15 to 200 g ft⁻³ (e.g. 50 to 150 g ft⁻³), still morepreferably 20 to 150 g ft⁻³.

Generally, the catalytic region comprises a total amount of the supportmaterial of 0.1 to 3.0 g in⁻³, preferably 0.2 to 2.5 g in⁻³, still morepreferably 0.3 to 2.0, and even more preferably 0.5 to 1.75 g in⁻³.

The catalytic region may be disposed or supported on the substrate. Itis preferred that the catalytic region is directly disposed or directlysupported on the substrate (i.e. the region is in direct contact with asurface of the substrate).

The oxidation catalyst may comprise a single catalytic region. Thecatalytic region may be a catalytic layer (e.g. a single catalyticlayer).

Alternatively, the oxidation catalyst may further comprise a secondcatalytic region, such as a second catalytic region described below. Thecatalytic region described above (i.e. the catalytic region comprisingbismuth) is referred to below as the first catalytic region. Thus, theoxidation catalyst comprises a first catalytic region and a secondcatalytic region. For the avoidance of doubt, the first catalytic regionis different (i.e. different composition) to the second catalyticregion.

The oxidation catalyst may further comprise a third catalytic region.When the oxidation catalyst comprises a third catalytic region, thethird catalytic region is different (i.e. different composition) to boththe first catalytic region and the second catalytic region.

In a first arrangement, the first catalytic region is a first catalyticlayer and the second catalytic region is a second catalytic layer. Thefirst catalytic layer may be disposed or supported (e.g. directlydisposed or supported) on the second catalytic layer. See, for example,FIG. 1. Alternatively, the second catalytic layer may be disposed orsupported (e.g. directly disposed or supported) on the first catalyticlayer. It is preferred that the first catalytic layer is disposed orsupported (e.g. directly disposed or supported) on the second catalyticlayer.

When the first catalytic layer is disposed or supported (e.g. directlydisposed or supported) on the second catalytic layer, then the secondcatalytic layer may be disposed or supported (e.g. directly disposed orsupported) on the substrate or on a third catalytic region, preferably athird catalytic layer. It is preferred that the second catalytic layermay be disposed or supported (e.g. directly disposed or supported) onthe substrate.

When the second catalytic layer is disposed or supported (e.g. directlydisposed or supported) on the first catalytic layer, then the firstcatalytic layer may be disposed or supported (e.g. directly disposed orsupported) on the substrate or on a third catalytic region, preferably athird catalytic layer. It is preferred that the first catalytic layermay be disposed or supported (e.g. directly disposed or supported) onthe substrate.

The first catalytic layer typically extends for an entire length (i.e.substantially an entire length) of the substrate, particularly theentire length of the channels of a substrate monolith.

The second catalytic layer typically extends for an entire length (i.e.substantially an entire length) of the substrate, particularly theentire length of the channels of a substrate monolith.

In the first arrangement, when the oxidation catalyst comprises a thirdcatalytic layer, then the third catalytic layer typically extends for anentire length (i.e. substantially an entire length) of the substrate,particularly the entire length of the channels of a substrate monolith.

In a second arrangement, the first catalytic region is a first catalyticzone and the second catalytic region is a second catalytic zone. Thefirst catalytic zone may be disposed upstream of the second catalyticzone. See, for example, FIG. 2. Alternatively, the second catalytic zonemay be disposed upstream of the first catalytic zone. It is preferredthat the first catalytic zone is disposed upstream of the secondcatalytic zone.

The first catalytic zone may adjoin the second catalytic zone or theremay be a gap (e.g. a space) between the first catalytic zone and thesecond catalytic zone. Preferably, the first catalytic zone is contactwith the second catalytic zone. When the first catalytic zone adjoinsand/or is in contact with the second catalytic zone, then thecombination of the first catalytic zone and the second catalytic zonemay be disposed or supported on the substrate as a layer (e.g. a singlelayer). Thus, a layer (e.g. a single) may be formed on the substratewhen the first and second catalytic zones adjoin or are in contact withone another. Such an arrangement may avoid problems with back pressure.

The first catalytic zone typically has a length of 10 to 90% of thelength of the substrate (e.g. 10 to 45%), preferably 15 to 75% of thelength of the substrate (e.g. 15 to 40%), more preferably 20 to 70%(e.g. 30 to 65%. such as 25 to 45%) of the length of the substrate,still more preferably 25 to 65% (e.g. 35 to 50%).

The second catalytic zone typically has a length of 10 to 90% of thelength of the substrate (e.g. 10 to 45%), preferably 15 to 75% of thelength of the substrate (e.g. 15 to 40%), more preferably 20 to 70%(e.g. 30 to 65%, such as 25 to 45%) of the length of the substrate,still more preferably 25 to 65% (e.g. 35 to 50%).

The first catalytic zone and the second catalytic zone may be disposedor supported (e.g. directly disposed or supported) on the substrate.Alternatively, the first catalytic zone and the second catalytic zonemay be disposed or supported (e.g. directly disposed or supported) on athird catalytic region, preferably a third catalytic layer. See, forexample, FIG. 6.

In the second arrangement, when the oxidation catalyst comprises a thirdcatalytic layer, then the third catalytic layer typically extends for anentire length (i.e. substantially an entire length) of the substrate,particularly the entire length of the channels of a substrate monolith.

In a third arrangement, the first catalytic region is disposed orsupported (e.g. directly disposed or supported) on the second catalyticregion.

The second catalytic region may be disposed or supported (e.g. directlydisposed or supported) on the substrate. Alternatively, the secondcatalytic region may be disposed or supported (e.g. directly disposed orsupported) on a third catalytic region, preferably a third catalyticlayer. It is preferred that the second catalytic region is disposed orsupported (e.g. directly disposed or supported) on the substrate.

An entire length (e.g. all) of the first catalytic region may bedisposed or supported (e.g. directly disposed or supported) on thesecond catalytic region. See, for example, FIG. 3. Alternatively, a partor portion of the length of the first catalytic region may be disposedor supported (e.g. directly disposed or supported) on the secondcatalytic region. A part or portion (e.g. the remaining part or portion)of the length of the first catalytic region may be disposed or supported(e.g. directly disposed or supported) on the substrate (see, forexample, FIGS. 4 and 5) or a third catalytic region, preferably a thirdcatalytic layer.

The second catalytic region may be a second catalytic layer and thefirst catalytic region may be a first catalytic zone. The entire lengthof the first catalytic zone is preferably disposed or supported on thesecond catalytic layer (e.g. see FIG. 3). The second catalytic layer maybe disposed or supported (e.g. directly disposed or supported) on thesubstrate or a third catalytic layer. It is preferred that the secondcatalytic layer is disposed or supported (e.g. directly disposed orsupported) on the substrate.

The second catalytic layer typically extends for an entire length (i.e.substantially an entire length) of the substrate, particularly theentire length of the channels of a substrate monolith.

The first catalytic zone typically has a length of 10 to 90% of thelength of the substrate (e.g. 10 to 45%), preferably 15 to 75% of thelength of the substrate (e.g. 15 to 40%), more preferably 20 to 70%(e.g. 30 to 65%, such as 25 to 45%) of the length of the substrate,still more preferably 25 to 65% (e.g. 35 to 50%).

The first catalytic zone may be disposed at or near an inlet end of thesubstrate (e.g. as shown in FIG. 3). The first catalytic zone may bedisposed at or near an outlet end of the substrate. It is preferred thatthe first catalytic zone is disposed at or near an inlet end of thesubstrate.

In an alternative third arrangement, the second catalytic region is asecond catalytic zone and the first catalytic region is a firstcatalytic zone or a first catalytic layer. The first catalytic zone orthe first catalytic layer is disposed or supported (e.g. directlydisposed or supported) on the second catalytic zone. See, for example,FIGS. 4 and 5.

The second catalytic zone typically has a length of 10 to 90% of thelength of the substrate (e.g. 10 to 45%), preferably 15 to 75% of thelength of the substrate (e.g. 15 to 40%), more preferably 20 to 70%(e.g. 30 to 65%, such as 25 to 45%) of the length of the substrate,still more preferably 25 to 65% (e.g. 35 to 50%).

An entire length (e.g. all) of the second catalytic zone may be disposedor supported (e.g. directly disposed or supported) on the substrate.Alternatively, an entire length (e.g. all) of the second catalytic zonemay be disposed or supported (e.g. directly disposed or supported) onthe third catalytic layer.

The second catalytic zone may be disposed at or near an outlet end ofthe substrate (e.g. as shown in FIGS. 4 and 5). The second catalyticzone may be disposed at or near an inlet end of the substrate. It ispreferred that the second catalytic zone is disposed at or near anoutlet end of the substrate.

In addition to being disposed or supported on the second catalytic zone,the first catalytic zone or the first catalytic layer may be disposed orsupported (e.g. directly disposed or supported) on the substrate or athird catalytic layer, preferably the substrate. Thus, a part or portionof the length of the first catalytic zone or the first catalytic layermay be disposed or supported (e.g. directly disposed or supported) onthe second catalytic zone and a part or portion (e.g. the remaining partor portion) of the length of the first catalytic zone or the firstcatalytic layer may be disposed or supported (e.g. directly disposed orsupported) on the substrate or the third catalytic layer, preferably thesubstrate.

In the alternative third arrangement, when the first catalytic region isa first catalytic zone (e.g. as shown in FIG. 4), then the firstcatalytic zone typically has a length of 10 to 90% of the length of thesubstrate (e.g. 10 to 45%), preferably 15 to 75% of the length of thesubstrate (e.g. 15 to 40%), more preferably 20 to 70% (e.g. 30 to 65%,such as 25 to 45%) of the length of the substrate, still more preferably25 to 65% (e.g. 35 to 50%).

The first catalytic zone may be disposed at or near an inlet end of thesubstrate (e.g. as shown in FIG. 4). The first catalytic zone may bedisposed at or near an outlet end of the substrate. It is preferred thatthe first catalytic zone is disposed at or near an outlet end of thesubstrate.

In the alternative third arrangement, when the first catalytic region isa first catalytic layer (e.g. as shown in FIG. 5), then the firstcatalytic layer typically extends for an entire length (i.e.substantially an entire length) of the substrate, particularly theentire length of the channels of a substrate monolith. When the firstcatalytic region is a first catalytic layer, then preferably the secondcatalytic zone is disposed at or near an outlet end of the substrate.

In a fourth arrangement, the second catalytic region is disposed orsupported on the first catalytic region.

The first catalytic region may be disposed or supported (e.g. directlydisposed or supported) on the substrate. Alternatively, the firstcatalytic region may be disposed or supported (e.g. directly disposed orsupported) on a third catalytic region, preferably a third catalyticlayer. It is preferred that the first catalytic region is disposed orsupported (e.g. directly disposed or supported) on the substrate.

An entire length (e.g. all) of the second catalytic region may bedisposed or supported (e.g. directly disposed or supported) on the firstcatalytic region. Alternatively, a part or portion of the length of thesecond catalytic region may be disposed or supported (e.g. directlydisposed or supported) on the first catalytic region. A part or portion(e.g. the remaining part or portion) of the length of the secondcatalytic region may be disposed or supported (e.g. directly disposed orsupported) on the substrate or a third catalytic region, preferably athird catalytic layer.

The first catalytic region may be a first catalytic layer and the secondcatalytic region may be a second catalytic zone. The entire length ofthe second catalytic zone is preferably disposed or supported on thefirst catalytic layer. The first catalytic layer may be disposed orsupported (e.g. directly disposed or supported) on the substrate or athird catalytic layer. It is preferred that the first catalytic layer isdisposed or supported (e.g. directly disposed or supported) on thesubstrate.

The first catalytic layer typically extends for an entire length (i.e.substantially an entire length) of the substrate, particularly theentire length of the channels of a substrate monolith.

The second catalytic zone typically has a length of 10 to 90% of thelength of the substrate (e.g. 10 to 45%), preferably 15 to 75% of thelength of the substrate (e.g. 15 to 40%), more preferably 20 to 70%(e.g. 30 to 65%, such as 25 to 45%) of the length of the substrate,still more preferably 25 to 65% (e.g. 35 to 50%).

The second catalytic zone may be disposed at or near an inlet end of thesubstrate (e.g. as shown in FIG. 3). The second catalytic zone may bedisposed at or near an outlet end of the substrate. It is preferred thatthe second catalytic zone is disposed at or near an outlet end of thesubstrate.

In an alternative fourth arrangement, the first catalytic region is afirst catalytic zone and the second catalytic region is a secondcatalytic zone or a second catalytic layer. The second catalytic zone orthe second catalytic layer is disposed or supported (e.g. directlydisposed or supported) on the first catalytic zone.

The first catalytic zone typically has a length of 10 to 90% of thelength of the substrate (e.g. 10 to 45%), preferably 15 to 75% of thelength of the substrate (e.g. 15 to 40%), more preferably 20 to 70%(e.g. 30 to 65%, such as 25 to 45%) of the length of the substrate,still more preferably 25 to 65% (e.g. 35 to 50%).

An entire length (e.g. all) of the first catalytic zone may be disposedor supported (e.g. directly disposed or supported) on the substrate.Alternatively, an entire length (e.g. all) of the first catalytic zonemay be disposed or supported (e.g. directly disposed or supported) onthe third catalytic layer.

The first catalytic zone may be disposed at or near an outlet end of thesubstrate. The first catalytic zone may be disposed at or near an inletend of the substrate. It is preferred that the first catalytic zone isdisposed at or near an inlet end of the substrate.

In addition to being disposed or supported on the first catalytic zone,the second catalytic zone or the second catalytic layer may be disposedor supported (e.g. directly disposed or supported) on the substrate or athird catalytic layer, preferably the substrate. Thus, a part or portionof the length of the second catalytic zone or the second catalytic layermay be disposed or supported (e.g. directly disposed or supported) onthe first catalytic zone and a part or portion (e.g. the remaining partor portion) of the length of the second catalytic zone or the secondcatalytic layer may be disposed or supported (e.g. directly disposed orsupported) on the substrate or the third catalytic layer, preferably thesubstrate.

In the alternative fourth arrangement, when the second catalytic regionis a second catalytic zone, then the second catalytic zone typically hasa length of 10 to 90% of the length of the substrate (e.g. 10 to 45%),preferably 15 to 75% of the length of the substrate (e.g. 15 to 40%),more preferably 20 to 70% (e.g. 30 to 65%, such as 25 to 45%) of thelength of the substrate, still more preferably 25 to 65% (e.g. 35 to50%).

The second catalytic zone may be disposed at or near an inlet end of thesubstrate. The second catalytic zone may be disposed at or near anoutlet end of the substrate. It is preferred that the second catalyticzone is disposed at or near an outlet end of the substrate.

In the alternative fourth arrangement, when the second catalytic regionis a second catalytic layer, then the second catalytic layer typicallyextends for an entire length (i.e. substantially an entire length) ofthe substrate, particularly the entire length of the channels of asubstrate monolith. When the second catalytic region is a secondcatalytic layer, then preferably the first catalytic zone is disposed ator near an inlet end of the substrate.

As a general feature of the third arrangement or the fourth arrangement,when the oxidation catalyst comprises a third catalytic layer, the thirdcatalytic layer typically extends for an entire length (i.e.substantially an entire length) of the substrate, particularly theentire length of the channels of a substrate monolith.

In the first to fourth arrangements above, the second catalytic region,layer or zone may have DOC activity, PNA activity or LNT activity, asdescribed below. When the oxidation catalyst comprises a third catalyticregion layer or zone, it is preferred that (i) the second catalyticregion, layer or zone has DOC activity and the third catalytic region,layer or zone has either PNA activity or LNT activity or (ii) the secondcatalytic region, layer or zone has either PNA activity or LNT activityand the third catalytic region, layer or zone has DOC activity. Morepreferably, the second catalytic region, layer or zone has DOC activityand the third catalytic region, layer or zone has either PNA activity orLNT activity. Even more preferably, the second catalytic region, layeror zone has DOC activity and the third catalytic region, layer or zonehas PNA activity.

The regions, zones and layers described hereinabove may be preparedusing conventional methods for making and applying washcoats onto asubstrate are also known in the art (see, for example, our WO 99/47260,WO 2007/077462 and WO 2011/080525).

Second Catalytic Region and/or Third Catalytic Region

The second catalytic region may be formulated to provide the oxidationcatalyst with additional functionality. The presence of the firstcatalytic region in combination with the second catalytic region mayenhance the activity of the oxidation catalyst as whole or the activityof the second catalytic region. This enhancement in activity may resultfrom a synergistic interaction between the first catalytic region andthe second catalytic region. The low CO light off temperature of thefirst catalytic region may generate an exotherm that is able to rapidlybring the second catalytic region up to its light off temperature.

The second catalytic region may have NO_(x) storage activity, such aslean NO_(x) trap (LNT) activity or passive NO_(x) absorber (PNA)activity. Additionally or alternatively, the second catalytic region maybe for oxidising hydrocarbons (HCs) and/or nitric oxide (NO) in theexhaust gas produced by the diesel engine (e.g. the second catalyticregion is a diesel oxidation catalytic region).

Catalytic Region Having PNA Activity

The second or third catalytic region may have PNA activity. A passiveNO_(x) absorber (PNA) is able to store or absorb NO_(x) at relativelylow exhaust gas temperatures (e.g. less than 200° C.), usually byadsorption, and release NO_(x) at higher temperatures. The NO_(x)storage and release mechanism of PNAs is thermally controlled, unlikethat of LNTs which require a rich purge to release stored NO_(x).

When the second or third catalytic region has NO_(x) storage activity(e.g. PNA activity), then the second or third catalytic regioncomprises, or consists essentially of, a molecular sieve catalystcomprising a noble metal and a molecular sieve, wherein the molecularsieve contains the noble metal.

The noble metal is typically selected from the group consisting ofpalladium (Pd), platinum (Pt) and rhodium (Rh). More preferably, thenoble metal is selected from palladium (Pd), platinum (Pt) and a mixturethereof.

Generally, it is preferred that the noble metal comprises, or consistsof, palladium (Pd) and optionally a second metal selected from the groupconsisting of platinum (Pt), rhodium (Rh), gold (Au), silver (Ag),iridium (Ir) and ruthenium (Ru). Preferably, the noble metal comprises,or consists of, palladium (Pd) and optionally a second metal selectedfrom the group consisting of platinum (Pt) and rhodium (Rh). Even morepreferably, the noble metal comprises, or consists of, palladium (Pd)and optionally platinum (Pt). More preferably, the molecular sievecatalyst comprises palladium as the only noble metal.

When the noble metal comprises, or consists of, palladium (Pd) and asecond metal, then the ratio by mass of palladium (Pd) to the secondmetal is >1:1. More preferably, the ratio by mass of palladium (Pd) tothe second metal is >1:1 and the molar ratio of palladium (Pd) to thesecond metal is >1:1.

The molecular sieve catalyst may further comprise a base metal. Thus,the molecular sieve catalyst may comprise, or consist essentially of, anoble metal, a molecular sieve and optionally a base metal. Themolecular sieve contains the noble metal and optionally the base metal.

The base metal may be selected from the group consisting of iron (Fe),copper (Cu), manganese (Mn), chromium (Cr), cobalt (Co), nickel (Ni),zinc (Zn) and tin (Sn), as well as mixtures of two or more thereof. Itis preferred that the base metal is selected from the group consistingof iron, copper and cobalt, more preferably iron and copper. Even morepreferably, the base metal is iron.

Alternatively, the molecular sieve catalyst may be substantially free ofa base metal, such as a base metal selected from the group consisting ofiron (Fe), copper (Cu), manganese (Mn), chromium (Cr), cobalt (Co),nickel (Ni), zinc (Zn) and tin (Sn), as well as mixtures of two or morethereof. Thus, the molecular sieve catalyst may not comprise a basemetal.

In general, it is preferred that the molecular sieve catalyst does notcomprise a base metal.

It may be preferable that the molecular sieve catalyst is substantiallyfree of barium (Ba), more preferably the molecular sieve catalyst issubstantially free of an alkaline earth metal. Thus, the molecular sievecatalyst may not comprise barium, preferably the molecular sievecatalyst does not comprise an alkaline earth metal.

The molecular sieve is typically composed of aluminium, silicon, and/orphosphorus. The molecular sieve generally has a three-dimensionalarrangement (e.g. framework) of SiO₄, AlO₄, and/or PO₄ that are joinedby the sharing of oxygen atoms. The molecular sieve may have an anionicframework. The charge of the anionic framework may be counterbalanced bycations, such as by cations of alkali and/or alkaline earth elements(e.g., Na, K, Mg, Ca, Sr, and Ba), ammonium cations and/or protons.

Typically, the molecular sieve has an aluminosilicate framework, analuminophosphate framework or a silico-aluminophosphate framework. Themolecular sieve may have an aluminosilicate framework or analuminophosphate framework. It is preferred that the molecular sieve hasan aluminosilicate framework or a silico-aluminophosphate framework.More preferably, the molecular sieve has an aluminosilicate framework.

When the molecular sieve has an aluminosilicate framework, then themolecular sieve is preferably a zeolite.

The molecular sieve contains the noble metal. The noble metal istypically supported on the molecular sieve. For example, the noble metalmay be loaded onto and supported on the molecular sieve, such as byion-exchange. Thus, the molecular sieve catalyst may comprise, orconsist essentially of, a noble metal and a molecular sieve, wherein themolecular sieve contains the noble metal and wherein the noble metal isloaded onto and/or supported on the molecular sieve by ion exchange.

In general, the molecular sieve may be a metal-substituted molecularsieve (e.g. metal-substituted molecular sieve having an aluminosilicateor an aluminophosphate framework). The metal of the metal-substitutedmolecular sieve may be the noble metal (e.g. the molecular sieve is anoble metal substituted molecular sieve). Thus, the molecular sievecontaining the noble metal may be a noble metal substituted molecularsieve. When the molecular sieve catalyst comprises a base metal, thenthe molecular sieve may be a noble and base metal-substituted molecularsieve. For the avoidance of doubt, the term “metal-substituted” embracesthe term “ion-exchanged”.

The molecular sieve catalyst generally has at least 1% by weight (i.e.of the amount of noble metal of the molecular sieve catalyst) of thenoble metal located inside pores of the molecular sieve, preferably atleast 5% by weight, more preferably at least 10% by weight, such as atleast 25% by weight, even more preferably at least 50% by weight.

The molecular sieve may be selected from a small pore molecular sieve(i.e. a molecular sieve having a maximum ring size of eight tetrahedralatoms), a medium pore molecular sieve (i.e. a molecular sieve having amaximum ring size of ten tetrahedral atoms) and a large pore molecularsieve (i.e. a molecular sieve having a maximum ring size of twelvetetrahedral atoms). More preferably, the molecular sieve is selectedfrom a small pore molecular sieve and a medium pore molecular sieve.

In a first molecular sieve catalyst embodiment, the molecular sieve is asmall pore molecular sieve. The small pore molecular sieve preferablyhas a Framework Type selected from the group consisting of ACO, AEI,AEN, AFN, AFT, AFX, ANA, APC, APD, ATT, CDO, CHA, DDR, DFT, EAB, EDI,EPI, ERI, GIS, GOO, IHW, ITE, ITW, LEV, KFI, MER, MON, NSI, OWE, PAU,PHI, RHO, RTH, SAT, SAV, SIV, THO, TSC, UEI, UFI, VNI, YUG and ZON, aswell as a mixture or intergrowth of any two or more thereof. Theintergrowth is preferably selected from KFI-SIV, ITE-RTH, AEW-UEI,AEI-CHA, and AEI-SAV. More preferably, the small pore molecular sievehas a Framework Type that is AEI, CHA or an AEI-CHA intergrowth. Evenmore preferably, the small pore molecular sieve has a Framework Typethat is AEI or CHA, particularly AEI.

Preferably, the small pore molecular sieve has an aluminosilicateframework or a silico-aluminophosphate framework. More preferably, thesmall pore molecular sieve has an aluminosilicate framework (i.e. themolecular sieve is a zeolite), especially when the small pore molecularsieve has a Framework Type that is AEI, CHA or an AEI-CHA intergrowth,particularly AEI or CHA.

In a second molecular sieve catalyst embodiment, the molecular sieve hasa Framework Type selected from the group consisting of AEI, MFI, EMT,ERI, MOR, FER, BEA, FAU, CHA, LEV, MWW, CON and EUO, as well as mixturesof any two or more thereof.

In a third molecular sieve catalyst embodiment, the molecular sieve is amedium pore molecular sieve. The medium pore molecular sieve preferablyhas a Framework Type selected from the group consisting of MFI, FER, MWWand EUO, more preferably MFI.

In a fourth molecular sieve catalyst embodiment, the molecular sieve isa large pore molecular sieve. The large pore molecular sieve preferablyhas a Framework Type selected from the group consisting of CON, BEA,FAU, MOR and EMT, more preferably BEA.

In each of the first to fourth molecular sieve catalyst embodiments, themolecular sieve preferably has an aluminosilicate framework (e.g. themolecular sieve is a zeolite). Each of the aforementioned three-lettercodes represents a framework type in accordance with the “IUPACCommission on Zeolite Nomenclature” and/or the “Structure Commission ofthe International Zeolite Association”.

The molecular sieve typically has a silica to alumina molar ratio (SAR)of 10 to 200 (e.g. 10 to 40), such as 10 to 100, more preferably 15 to80 (e.g. 15 to 30). The SAR generally relates to a molecular having analuminosilicate framework (e.g. a zeolite) or a silico-aluminophosphateframework, preferably an aluminosilicate framework (e.g. a zeolite).

The molecular sieve catalyst of the first, third and fourth molecularsieve catalyst embodiments (and also for some of the Framework Types ofthe second molecular sieve catalyst embodiment), particularly when themolecular sieve is a zeolite, may have an infrared spectrum having acharacteristic absorption peak in a range of from 750 cm⁻¹ to 1050 cm⁻¹(in addition to the absorption peaks for the molecular sieve itself).Preferably, the characteristic absorption peak is in the range of from800 cm⁻¹ to 1000 cm⁻¹, more preferably in the range of from 850 cm⁻¹ to975 cm⁻¹.

The molecular sieve catalyst of the first molecular sieve catalystembodiment has been found to have advantageous passive NO_(x) adsorber(PNA) activity. The molecular sieve catalyst can be used to store NO_(x)when exhaust gas temperatures are relatively cool, such as shortly afterstart-up of a lean burn engine. NO_(x) storage by the molecular sievecatalyst occurs at low temperatures (e.g. less than 200° C.). As thelean burn engine warms up, the exhaust gas temperature increases and thetemperature of the molecular sieve catalyst will also increase. Themolecular sieve catalyst will release adsorbed NO_(x) at these highertemperatures (e.g. 200° C. or above).

The second molecular sieve catalyst embodiment has cold start catalystactivity. Such activity can reduce emissions during the cold startperiod by adsorbing NO_(x) and hydrocarbons (HCs) at relatively lowexhaust gas temperatures (e.g. less than 200° C.). Adsorbed NO_(x)and/or HCs can be released when the temperature of the molecular sievecatalyst is close to or above the effective temperature of the othercatalyst components or emissions control devices for oxidising NO and/orHCs.

When the second or third catalytic region has PNA activity, thentypically the second or third catalytic region comprises a total loadingof noble metal of 1 to 250 g ft⁻³, preferably 5 to 150 g ft⁻³, morepreferably 10 to 100 g ft⁻³.

Catalytic Region Having LNT Activity

The second or third catalytic region may have LNT activity. Duringnormal operation, a diesel engine produces an exhaust gas having a“lean” composition. An LNT comprises a NO_(x) storage component that isable to store or trap nitrogen oxides (NO_(x)) from the exhaust gas byforming an inorganic nitrate. To release the NO_(x) from the NO_(x)storage component, such as when the NO_(x) storage component is about toreach its storage capacity, the diesel engine may be run under richconditions to produce an exhaust gas having a “rich” composition. Underthese conditions, the inorganic nitrates of the NO_(x) storage componentdecompose and form mainly nitrogen dioxide (NO₂) and some nitric oxide(NO). The LNT may contain a platinum group metal component that is ableto catalytically reduce the released NO_(x) to N₂ or NH₃ withhydrocarbons (HCs), carbon monoxide (CO) or hydrogen (H₂) present in theexhaust gas.

When the second or third catalytic region has NO_(x) storage activity(e.g. LNT activity), then the second or third catalytic regioncomprises, or consists essentially of, a nitrogen oxides (NO_(x))storage material. The nitrogen oxides (NO_(x)) storage materialcomprises, or consists essentially of, a nitrogen oxides (NO_(x))storage component on a support material. It is preferred that the secondcatalytic region further comprises at least one platinum group metal(PGM). The at least one platinum group metal (PGM) may be provided bythe NO_(x) treatment material described herein below.

The NO_(x) storage material comprises, or may consist essentially of, aNO_(x) storage component on a support material.

The NO_(x) storage component typically comprises an alkali metal, analkaline earth metal and/or a rare earth metal. The NO_(x) storagecomponent generally comprises, or consists essentially of, (i) an oxide,a carbonate or a hydroxide of an alkali metal; (ii) an oxide, acarbonate or a hydroxide of an alkaline earth metal; and/or (iii) anoxide, a carbonate or a hydroxide of a rare earth metal.

When the NO_(x) storage component comprises an alkali metal (or anoxide, a carbonate or a hydroxide thereof), then preferably the alkalimetal is selected from the group consisting of potassium (K), sodium(Na), lithium (Li), caesium (Cs) and a combination of two or morethereof. It is preferred that the alkali metal is potassium (K), sodium(Na) or lithium (Li), more preferably the alkali metal is potassium (K)or sodium (Na), and most preferably the alkali metal is potassium (K).

When the NO_(x) storage component comprises an alkaline earth metal (oran oxide, a carbonate or a hydroxide thereof), then preferably thealkaline earth metal is selected from the group consisting of magnesium(Mg), calcium (Ca), strontium (Sr), barium (Ba) and a combination of twoor more thereof. It is preferred that the alkaline earth metal iscalcium (Ca), strontium (Sr), or barium (Ba), more preferably strontium(Sr) or barium (Ba), and most preferably the alkaline earth metal isbarium (Ba).

When the NO_(x) storage component comprises a rare earth metal (or anoxide, a carbonate or a hydroxide thereof), then preferably the rareearth metal is selected from the group consisting of cerium (Ce),lanthanum (La), yttrium (Y) and a combination thereof. More preferably,the rare earth metal is cerium (Ce).

Typically, the NO_(x) storage component comprises, or consistsessentially of, (i) an oxide, a carbonate or a hydroxide of a rare earthmetal and/or (ii) an oxide, a carbonate or a hydroxide of an alkalineearth metal. It is preferred that the NO_(x) storage componentcomprises, or consists essentially of, an oxide, a carbonate or ahydroxide of an alkaline earth metal.

It is preferred that the NO_(x) storage component comprises barium (Ba)(e.g. an oxide, a carbonate or a hydroxide of barium (Ba)). Morepreferably, the NO_(x) storage component comprises barium (e.g. anoxide, a carbonate or a hydroxide of barium (Ba)) and cerium (e.g. anoxide, a carbonate or a hydroxide of cerium (Ce), preferably ceria).

Typically, the NO_(x) storage component is disposed or supported on thesupport material. The NO_(x) storage component may be disposed directlyonto or is directly supported by the support material (e.g. there is nointervening support material between the NO_(x) storage component andthe support material).

The support material generally comprises an oxide of aluminium.Typically, the support material comprises alumina. The alumina may ormay not be doped with a dopant.

The alumina may be doped with a dopant selected from the groupconsisting of silicon (Si), magnesium (Mg), barium (Ba), lanthanum (La),cerium (Ce), titanium (Ti), zirconium (Zr) and a combination of two ormore thereof. It is preferred that the dopant is selected from the groupconsisting of silicon (Si), magnesium (Mg), barium (Ba) and cerium (Ce).More preferably, the dopant is selected from the group consisting ofsilicon (Si), magnesium (Mg) and barium (Ba). Even more preferably, thedopant is magnesium (Mg).

When the alumina is doped, the total amount of dopant is 0.25 to 5% byweight, preferably 0.5 to 3% by weight (e.g. about 1% by weight) of thealumina.

In general, it is preferred that the support material comprises, orconsists essentially of, an oxide of magnesium and aluminium. The oxideof magnesium and aluminium may comprise, or consist essentially of,magnesium aluminate (MgAl₂O₄ [e.g. spinel]) and/or a mixed oxide ofmagnesium oxide (MgO) and aluminium oxide (Al₂O₃). A mixed oxide ofmagnesium oxide and aluminium oxide can be prepared using methods knownin the art, such as by using the processes described in U.S. Pat. No.6,217,837 or DE 19503522 A1.

The mixed oxide of magnesium oxide (MgO) and aluminium oxide (Al₂O₃)typically comprises, or consists essentially of, 1.0 to 40.0% by weightof magnesium oxide (based on the total weight of the mixed oxide), suchas 1.0 to 30.0% by weight, preferably 5.0 to 28.0% by weight (e.g. 5.0to 25.0% by weight), more preferably 10.0 to 25.0% by weight ofmagnesium oxide.

The mixed oxide of magnesium oxide (MgO) and aluminium oxide (Al₂O₃) istypically a homogeneous mixed oxide of magnesium oxide (MgO) andaluminium oxide (Al₂O₃). In a homogeneous mixed oxide, magnesium ionsoccupy the positions within the lattice of aluminium ions.

Generally, a support material comprising, or consisting essentially of,a mixed oxide of magnesium oxide (MgO) and aluminium oxide (Al₂O₃) ispreferred.

The NO_(x) storage material may further comprise a platinum group metal(PGM). The PGM may be selected from the group consisting of platinum,palladium, rhodium and a combination of any two or more thereof.Preferably, the PGM is selected from platinum, palladium and acombination of platinum and palladium.

When the NO_(x) storage material comprises a PGM, then generally the PGMis disposed or supported on the support material. The PGM is preferablydisposed directly onto or is directly supported by the support material(e.g. there is no intervening support material between the PGM and thesupport material).

Typically, the second or third catalytic region further comprises aNO_(x) treatment material. For the avoidance of doubt, the NO_(x)treatment material is different (e.g. different composition) to theNO_(x) storage material. The NO_(x) treatment material may have (a)NO_(x) storage activity and/or NO oxidative activity [e.g. under leanconditions]; and/or (b) NO_(x) reductive activity [e.g. under richconditions].

The NO_(x) treatment material comprises, or consists essentially of, aNO_(x) treatment component.

Typically, the NO_(x) treatment component (NTC) comprises a supportmaterial. The support material of the NO_(x) treatment component (NTC)is referred to herein as the NTC support material.

The NTC support material comprises, or consists essentially of, ceria,or a mixed or composite oxide of ceria, such as a ceria-zirconia.

When the NTC support material comprises, or consists essentially of, aceria-zirconia, then the ceria-zirconia may consist essentially of 20 to95% by weight of ceria and 5 to 80% by weight of zirconia (e.g. 50 to95% by weight ceria and 5 to 50% by weight zirconia), preferably 35 to80% by weight of ceria and 20 to 65% by weight zirconia (e.g. 55 to 80%by weight ceria and 20 to 45% by weight zirconia), even more preferably45 to 75% by weight of ceria and 25 to 55% by weight zirconia.

In general, the NO_(x) treatment component may comprise a platinum groupmetal (PGM) and/or a NO_(x) storage component.

The NO_(x) treatment component may comprise, or consist essentially of,a platinum group metal (PGM) disposed or supported (e.g. directlydisposed or supported) on the first support material. The PGM may beselected from the group consisting of platinum, palladium, rhodium, acombination of platinum and palladium, a combination of platinum andrhodium, a combination of palladium and rhodium, and a combination ofplatinum, palladium and rhodium. It is preferred that the PGM isselected from the group consisting of palladium, rhodium and acombination of palladium and rhodium.

The PGM (i.e. of the NO_(x) treatment component) may be rhodium. The PGMmay be palladium. Preferably, the PGM is palladium.

Additionally or alternatively, the NO_(x) treatment component maycomprise, or consist essentially of, a NO_(x) storage component disposedor supported (e.g. directly disposed or supported) on the NTC supportmaterial. The NO_(x) storage component generally comprises, or consistsessentially of, (i) an oxide, a carbonate or a hydroxide of an alkalimetal; (ii) an oxide, a carbonate or a hydroxide of an alkaline earthmetal; and/or (iii) an oxide, a carbonate or a hydroxide of a rare earthmetal, preferably a rare earth metal other than cerium (Ce). It ispreferred that the NO_(x) storage component comprises, or consistsessentially of, an oxide, a carbonate or a hydroxide of an alkalineearth metal. The alkaline earth metal is preferably barium (Ba).

Catalytic Region Having DOC Activity

The second or third catalytic region may be for oxidising hydrocarbons(HCs) and/or nitric oxide (NO) in the exhaust gas produced by the dieselengine (e.g. the second or third catalytic region is a diesel oxidationcatalytic region or has diesel oxidation catalyst (DOC) activity).

When the second or third catalytic region is for oxidising hydrocarbons(HCs) and/or nitric oxide (NO) in the exhaust gas produced by the dieselengine, the second or third catalytic region comprises platinum (Pt) anda support material. It is particularly preferred that the second orthird catalytic region comprises, or consists essentially of, platinum(Pt), manganese (Mn) and a support material. The second or thirdcatalytic region is for oxidising hydrocarbons (HCs) and/or nitric oxide(NO) in the exhaust gas produced by the diesel engine

The platinum (Pt) is typically disposed or supported on the supportmaterial. The platinum may be disposed directly onto or is directlysupported by the support material (e.g. there is no intervening supportmaterial between the platinum and the support material). For example,platinum can be dispersed on the support material.

The second or third catalytic region may further comprise palladium,such as palladium disposed or supported on the support material. Whenthe second or third catalytic region comprises palladium, then the ratioof platinum to palladium by total weight is generally ≥2:1 (e.g. Pt:Pd1:0 to 2:1), more preferably ≥4:1 (e.g. Pt:Pd 1:0 to 4:1).

It is generally preferred that the second or third catalytic region issubstantially free of palladium, particularly substantially free ofpalladium (Pd) disposed or supported on the support material. Morepreferably, the second or third catalytic region does not comprisepalladium, particularly palladium disposed or supported on the supportmaterial. The presence of palladium, particularly in a large amount, inthe second catalytic region can be detrimental to NO oxidation activity.The NO oxidising activity of palladium is generally poor under thetypical usage conditions for a diesel oxidation catalyst. Also, anypalladium that is present may react with some of the platinum that ispresent to form an alloy. This can also be detrimental to the NOoxidation activity of the second catalytic region becauseplatinum-palladium alloys are not as active toward NO oxidation asplatinum is by itself.

Generally, the second or third catalytic region comprises platinum (Pt)as the only platinum group metal. The second or third catalytic regionpreferably does not comprise one or more other platinum group metals,such as ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os) and/oriridium (Ir).

The second or third catalytic region typically has a total loading ofplatinum of 5 to 300 g ft⁻³. It is preferred that the second or thirdcatalytic region has a total loading of platinum of 10 to 250 g ft⁻³(e.g. 75 to 175 g ft⁻³), more preferably 15 to 200 g ft⁻³ (e.g. 50 to150 g ft⁻³), still more preferably 20 to 150 g ft⁻³.

It is preferable that a primary function of the second or thirdcatalytic region is oxidising nitric oxide (NO) to nitrogen dioxide(NO₂). However, it is appreciated that in some embodiments of theoxidation catalyst, the second or third catalytic region will alsooxidise some hydrocarbons (HCs) during use.

The second or third catalytic region may also comprise manganese (Mn).The manganese may be present in an elemental form or as an oxide. Thesecond or third catalytic region typically comprises manganese or anoxide thereof.

The manganese (Mn) is typically disposed or supported on the supportmaterial. The manganese (Mn) may be disposed directly onto or isdirectly supported by the support material (e.g. there is no interveningsupport material between the Mn and the support material).

The second or third catalytic region typically has a total loading ofmanganese (Mn) of 5 to 500 g ft⁻³. It is preferred that the second orthird catalytic region has a total loading of manganese (Mn) of 10 to250 g ft⁻³ (e.g. 75 to 175 g ft⁻³), more preferably 15 to 200 g ft⁻³(e.g. 50 to 150 g ft⁻³), still more preferably 20 to 150 g ft⁻³.

Typically, the second or third catalytic region comprises a ratio ofMn:Pt by weight of ≤5:1, more preferably <5:1.

In general, the second or third catalytic region comprises a ratio ofMn:Pt by weight of ≥0.2:1 (e.g. ≥0.5:1), more preferably >0.2:1 (e.g.>0.5:1).

The second or third catalytic region may comprise a ratio by totalweight of manganese (Mn) to platinum of 5:1 to 0.2:1, such as 5:1 to0.5:1 (e.g. 5:1 to 2:3 or 5:1 to 1:2), preferably 4.5:1 to 1:1 (e.g. 4:1to 1.1:1), more preferably 4:1 to 1.5:1. The ratio of Mn:Pt by weightcan be important in obtaining advantageous NO oxidation activity.

Typically, the support material comprises, or consists essentially of, arefractory oxide.

The refractory oxide is typically selected from the group consisting ofalumina, silica, titania, zirconia, ceria and a mixed or composite oxidethereof, such as a mixed or composite oxide of two or more thereof. Forexample, the refractory oxide may be selected from the group consistingof alumina, silica, titania, zirconia, ceria, silica-alumina,titania-alumina, zirconia-alumina, ceria-alumina, titania-silica.zirconia-silica, zirconia-titania, ceria-zirconia and alumina-magnesiumoxide.

The support material, or the refractory oxide thereof, may optionally bedoped (e.g. with a dopant). The dopant may be selected from the groupconsisting of zirconium (Zr), titanium (Ti), silicon (Si), yttrium (Y),lanthanum (La), praseodymium (Pr), samarium (Sm), neodymium (Nd) and anoxide thereof.

When the support material, or the refractory oxide thereof, is doped,the total amount of dopant is 0.25 to 5% by weight, preferably 0.5 to 3%by weight (e.g. about 1% by weight).

The support material, or the refractory oxide thereof, may comprise, orconsist essentially of, alumina doped with a dopant. It is particularlypreferred that the support material, or the refractory oxide thereof,comprises, or consists essentially of, alumina doped with a dopant. Ithas been found that the combination of manganese (Mn), platinum (Pt) anda doped alumina support material, particularly an alumina supportmaterial doped with silica, provides excellent NO oxidation activity andcan stabilise NO oxidation activity of the oxidation catalyst over itslifetime.

The alumina may be doped with a dopant comprising silicon (Si),magnesium (Mg), barium (Ba), lanthanum (La), cerium (Ce), titanium (Ti),or zirconium (Zr) or a combination of two or more thereof. The dopantmay comprise, or consist essentially of, an oxide of silicon, an oxideof magnesium, an oxide of barium, an oxide of lanthanum, an oxide ofcerium, an oxide of titanium or an oxide of zirconium. Preferably, thedopant comprises, or consists essentially of, silicon, magnesium,barium, cerium, or an oxide thereof; particularly silicon, cerium, or anoxide thereof. More preferably, the dopant comprises, or consistsessentially of, silicon, magnesium, barium, or an oxide thereof;particularly silicon, magnesium, or an oxide thereof; especially siliconor an oxide thereof.

Examples of alumina doped with a dopant include alumina doped withsilica, alumina doped with magnesium oxide, alumina doped with barium orbarium oxide, alumina doped with lanthanum oxide, or alumina doped withceria, particularly alumina doped with silica, alumina doped withlanthanum oxide, or alumina doped with ceria. It is preferred that thealumina doped with a dopant is alumina doped with silica, alumina dopedwith barium or barium oxide, or alumina doped with magnesium oxide. Morepreferably, the alumina doped with a dopant is alumina doped with silicaor alumina doped with magnesium oxide. Even more preferably, the aluminadoped with a dopant is alumina doped with silica.

When the alumina is alumina doped with silica, then the alumina is dopedwith silica in a total amount of 0.5 to 45% by weight (i.e. % by weightof the alumina), preferably 1 to 40% by weight, more preferably 1.5 to30% by weight (e.g. 1.5 to 10% by weight), particularly 2.5 to 25% byweight, more particularly 3.5 to 20% by weight (e.g. 5 to 20% byweight), even more preferably 4.5 to 15% by weight.

When the alumina is alumina doped with magnesium oxide, then the aluminais doped with magnesium in an amount as defined above or an amount of 1to 30% by weight (i.e. % by weight of the alumina), preferably 5 to 25%by weight.

It is preferred that the support material, or the refractory oxidethereof, is not doped with a dopant comprising, or consistingessentially of, manganese. Thus, the support material, or the refractoryoxide thereof, is not promoted with a promoter, such as a promoterselected from the group consisting of tin, manganese, indium, group VIIImetal (e.g. Fe. Co, Ni, Ru, Rh, Pd, Os, Ir and Pt, particularly Ir) andcombinations thereof.

In general, when the support material, or the refractory oxide thereof,comprises or consists essentially of a mixed or composite oxide ofalumina (e.g. silica-alumina, alumina-magnesium oxide or a mixture ofalumina and ceria), then preferably the mixed or composite oxide ofalumina comprises at least 50 to 99% by weight of alumina, morepreferably 70 to 95% by weight of alumina, even more preferably 75 to90% by weight of alumina.

When the support material, or refractory oxide thereof, comprises orconsists essentially of ceria-zirconia, then the ceria-zirconia mayconsist essentially of 20 to 95% by weight of ceria and 5 to 80% byweight of zirconia (e.g. 50 to 95% by weight ceria and 5 to 50% byweight zirconia), preferably 35 to 80% by weight of ceria and 20 to 65%by weight zirconia (e.g. 55 to 80% by weight ceria and 20 to 45% byweight zirconia), even more preferably 45 to 75% by weight of ceria and25 to 55% by weight zirconia. Typically, the second or third catalyticregion comprises an amount of the support material of 0.1 to 4.5 g in⁻³(e.g. 0.25 to 4.0 g in⁻³), preferably 0.5 to 3.0 g in⁻³, more preferably0.6 to 2.5 g in⁻³ (e.g. 0.75 to 1.5 g in⁻³).

In some applications, it may generally be preferable that the second orthird catalytic region is substantially free of a hydrocarbon adsorbentmaterial, particularly a zeolite. Thus, the second or third catalyticregion may not comprise a hydrocarbon adsorbent material.

The second or third catalytic region typically does not comprise indiumand/or iridium. More preferably, the second or third catalytic regiondoes not comprise indium, iridium and/or magnesium.

It may be preferable that the second or third catalytic region does notcomprise cerium oxide or a mixed or composite oxide thereof, such as (i)a mixed or composite oxide of cerium oxide and alumina and/or (ii) amixed or composite oxide of cerium oxide and zirconia.

Additionally or alternatively, the second or third catalytic region maybe substantially free of rhodium, an alkali metal and/or an alkalineearth metal, particularly an alkali metal and/or an alkaline earth metaldisposed or supported on the support material. Thus, the second or thirdcatalytic region may not comprise rhodium, an alkali metal and/or analkaline earth metal, particularly an alkali metal and/or an alkalineearth metal disposed or supported on the support material.

Substrate

The oxidation catalyst of the invention comprises a substrate. Thesubstrate typically has an inlet end and an outlet end.

In general, the substrate has a plurality of channels (e.g. for theexhaust gas to flow through). Generally, the substrate is a ceramicmaterial or a metallic material.

It is preferred that the substrate is made or composed of cordierite(SiO₂—Al₂O₃—MgO), silicon carbide (SiC), Fe—Cr—Al alloy, Ni—Cr—Al alloy,or a stainless steel alloy.

Typically, the substrate is a monolith (also referred to herein as asubstrate monolith). Such monoliths are well-known in the art.

The substrate monolith may be a flow-through monolith. Alternatively,the substrate may be a filtering monolith.

A flow-through monolith typically comprises a honeycomb monolith (e.g. ametal or ceramic honeycomb monolith) having a plurality of channelsextending therethrough, which each channel is open at the inlet end andthe outlet end.

A filtering monolith generally comprises a plurality of inlet channelsand a plurality of outlet channels, wherein the inlet channels are openat an upstream end (i.e. exhaust gas inlet side) and are plugged orsealed at a downstream end (i.e. exhaust gas outlet side), the outletchannels are plugged or sealed at an upstream end and are open at adownstream end, and wherein each inlet channel is separated from anoutlet channel by a porous structure.

When the monolith is a filtering monolith, it is preferred that thefiltering monolith is a wall-flow filter. In a wall-flow filter, eachinlet channel is alternately separated from an outlet channel by a wallof the porous structure and vice versa. It is preferred that the inletchannels and the outlet channels are arranged in a honeycombarrangement. When there is a honeycomb arrangement, it is preferred thatthe channels vertically and laterally adjacent to an inlet channel areplugged at an upstream end and vice versa (i.e. the channels verticallyand laterally adjacent to an outlet channel are plugged at a downstreamend). When viewed from either end, the alternately plugged and open endsof the channels take on the appearance of a chessboard.

In principle, the substrate may be of any shape or size. However, theshape and size of the substrate is usually selected to optimise exposureof the catalytically active materials in the catalyst to the exhaustgas. The substrate may, for example, have a tubular, fibrous orparticulate form. Examples of suitable supporting substrates include asubstrate of the monolithic honeycomb cordierite type, a substrate ofthe monolithic honeycomb SiC type, a substrate of the layered fibre orknitted fabric type, a substrate of the foam type, a substrate of thecrossflow type, a substrate of the metal wire mesh type, a substrate ofthe metal porous body type and a substrate of the ceramic particle type.

Exhaust System

The invention also provides an exhaust system comprising the oxidationcatalyst and an emissions control device. Examples of an emissionscontrol device include a diesel particulate filter (DPF), a lean NO_(x)trap (LNT), a lean NO_(x) catalyst (LNC), a selective catalyticreduction (SCR) catalyst, a diesel oxidation catalyst (DOC), a catalysedsoot filter (CSF), a selective catalytic reduction filter (SCRF™)catalyst, an ammonia slip catalyst (ASC) and combinations of two or morethereof. Such emissions control devices are all well known in the art.

Some of the aforementioned emissions control devices have filteringsubstrates. An emissions control device having a filtering substrate maybe selected from the group consisting of a diesel particulate filter(DPF), a catalysed soot filter (CSF), and a selective catalyticreduction filter (SCRF™) catalyst.

It is preferred that the exhaust system comprises an emissions controldevice selected from the group consisting of a lean NO_(x) trap (LNT),an ammonia slip catalyst (ASC), diesel particulate filter (DPF), aselective catalytic reduction (SCR) catalyst, a catalysed soot filter(CSF), a selective catalytic reduction filter (SCRF™) catalyst, andcombinations of two or more thereof. More preferably, the emissionscontrol device is selected from the group consisting of a dieselparticulate filter (DPF), a selective catalytic reduction (SCR)catalyst, a catalysed soot filter (CSF), a selective catalytic reductionfilter (SCRF™) catalyst, and combinations of two or more thereof. Evenmore preferably, the emissions control device is a selective catalyticreduction (SCR) catalyst or a selective catalytic reduction filter(SCRF™) catalyst.

When the exhaust system of the invention comprises an SCR catalyst or anSCRF™ catalyst, then the exhaust system may further comprise an injectorfor injecting a nitrogenous reductant, such as ammonia, or an ammoniaprecursor, such as urea or ammonium formate, preferably urea, intoexhaust gas downstream of the oxidation catalyst and upstream of the SCRcatalyst or the SCRF™ catalyst. Such an injector may be fluidly linkedto a source (e.g. a tank) of a nitrogenous reductant precursor.Valve-controlled dosing of the precursor into the exhaust gas may beregulated by suitably programmed engine management means and closed loopor open loop feedback provided by sensors monitoring the composition ofthe exhaust gas. Ammonia can also be generated by heating ammoniumcarbamate (a solid) and the ammonia generated can be injected into theexhaust gas.

Alternatively or in addition to the injector, ammonia can be generatedin situ (e.g. during rich regeneration of a LNT disposed upstream of theSCR catalyst or the SCRF™ catalyst). Thus, the exhaust system mayfurther comprise an engine management means for enriching the exhaustgas with hydrocarbons.

The SCR catalyst or the SCRF™ catalyst may comprise a metal selectedfrom the group consisting of at least one of Cu, Hf, La, Au, In, V,lanthanides and Group VIII transition metals (e.g. Fe), wherein themetal is supported on a refractory oxide or molecular sieve. The metalis preferably selected from Ce, Fe, Cu and combinations of any two ormore thereof, more preferably the metal is Fe or Cu.

The refractory oxide for the SCR catalyst or the SCRF™ catalyst may beselected from the group consisting of Al₂O₃, TiO₂, CeO₂, SiO₂, ZrO₂ andmixed oxides containing two or more thereof. The non-zeolite catalystcan also include tungsten oxide (e.g. V₂O₅/WO₃/TiO₂, WO_(x)/CeZrO₂,WO_(x)/ZrO₂ or Fe/WO_(x)/ZrO₂).

It is particularly preferred when an SCR catalyst, an SCRF™ catalyst ora washcoat thereof comprises at least one molecular sieve, such as analuminosilicate zeolite or a SAPO. The at least one molecular sieve canbe a small, a medium or a large pore molecular sieve. By “small poremolecular sieve” herein we mean molecular sieves containing a maximumring size of 8, such as CHA; by “medium pore molecular sieve” herein wemean a molecular sieve containing a maximum ring size of 10, such asZSM-5; and by “large pore molecular sieve” herein we mean a molecularsieve having a maximum ring size of 12, such as beta. Small poremolecular sieves are potentially advantageous for use in SCR catalysts.

In the exhaust system of the invention, preferred molecular sieves foran SCR catalyst or an SCRF™ catalyst are synthetic aluminosilicatezeolite molecular sieves selected from the group consisting of AEI,ZSM-5, ZSM-20, ERI including ZSM-34, mordenite, ferrierite, BEAincluding Beta, Y, CHA, LEV including Nu-3, MCM-22 and EU-1, preferablyAEI or CHA, and having a silica-to-alumina ratio of about 10 to about50, such as about 15 to about 40.

In a first exhaust system embodiment, the exhaust system comprises theoxidation catalyst of the invention and a catalysed soot filter (CSF).The oxidation catalyst may comprise a second catalytic region havingPNA. LNT and/or DOC activity. The oxidation catalyst is typicallyfollowed by (e.g. is upstream of) the catalysed soot filter (CSF). Thus,for example, an outlet of the oxidation catalyst is connected to aninlet of the catalysed soot filter.

A second exhaust system embodiment relates to an exhaust systemcomprising the oxidation catalyst of the invention, a catalysed sootfilter (CSF) and a selective catalytic reduction (SCR) catalyst. Theoxidation catalyst may comprise a second catalytic region having PNA,LNT and/or DOC activity. Such an arrangement is a preferred exhaustsystem for a light-duty diesel vehicle.

The oxidation catalyst is typically followed by (e.g. is upstream of)the catalysed soot filter (CSF). The catalysed soot filter is typicallyfollowed by (e.g. is upstream of) the selective catalytic reduction(SCR) catalyst. A nitrogenous reductant injector may be arranged betweenthe catalysed soot filter (CSF) and the selective catalytic reduction(SCR) catalyst. Thus, the catalysed soot filter (CSF) may be followed by(e.g. is upstream of) a nitrogenous reductant injector, and thenitrogenous reductant injector may be followed by (e.g. is upstream of)the selective catalytic reduction (SCR) catalyst.

In a third exhaust system embodiment, the exhaust system comprises theoxidation catalyst of the invention, a selective catalytic reduction(SCR) catalyst and either a catalysed soot filter (CSF) or a dieselparticulate filter (DPF). The oxidation catalyst may comprise a secondcatalytic region having PNA, LNT and/or DOC activity.

In the third exhaust system embodiment, the oxidation catalyst of theinvention is typically followed by (e.g. is upstream of) the selectivecatalytic reduction (SCR) catalyst. A nitrogenous reductant injector maybe arranged between the oxidation catalyst and the selective catalyticreduction (SCR) catalyst. Thus, the oxidation catalyst may be followedby (e.g. is upstream of) a nitrogenous reductant injector, and thenitrogenous reductant injector may be followed by (e.g. is upstream of)the selective catalytic reduction (SCR) catalyst. The selectivecatalytic reduction (SCR) catalyst are followed by (e.g. are upstreamof) the catalysed soot filter (CSF) or the diesel particulate filter(DPF).

A fourth exhaust system embodiment comprises the oxidation catalyst ofthe invention and a selective catalytic reduction filter (SCRF™)catalyst. The oxidation catalyst of the invention is typically followedby (e.g. is upstream of) the selective catalytic reduction filter(SCRF™) catalyst. The oxidation catalyst may comprise a second catalyticregion having PNA, LNT and/or DOC activity.

A nitrogenous reductant injector may be arranged between the oxidationcatalyst and the selective catalytic reduction filter (SCRF™) catalyst.Thus, the oxidation catalyst may be followed by (e.g. is upstream of) anitrogenous reductant injector, and the nitrogenous reductant injectormay be followed by (e.g. is upstream of) the selective catalyticreduction filter (SCRF™) catalyst.

When the exhaust system comprises a selective catalytic reduction (SCR)catalyst or a selective catalytic reduction filter (SCRF™) catalyst,such as in the second to fourth exhaust system embodiments describedhereinabove, an ASC can be disposed downstream from the SCR catalyst orthe SCRF™ catalyst (i.e. as a separate substrate monolith), or morepreferably a zone on a downstream or trailing end of the substratemonolith comprising the SCR catalyst can be used as a support for theASC.

In general, the exhaust system of the invention may comprise ahydrocarbon supply apparatus (e.g. for generating a rich exhaust gas),particularly when the second catalytic region of the oxidation catalysthas LNT activity. The hydrocarbon supply apparatus may be disposedupstream of the catalyst of the invention. The hydrocarbon supplyapparatus is typically disposed downstream of the exhaust outlet of thediesel engine.

The hydrocarbon supply apparatus may be electronically coupled to anengine management system, which is configured to inject hydrocarbon intothe exhaust gas for releasing NO_(x) (e.g. stored NO_(x)) from thecatalyst.

The hydrocarbon supply apparatus may be an injector. The hydrocarbonsupply apparatus or injector is suitable for injecting fuel into theexhaust gas.

Alternatively or in addition to the hydrocarbon supply apparatus, thediesel engine may comprise an engine management system (e.g. an enginecontrol unit [ECU]). The engine management system is configured forin-cylinder injection of the hydrocarbon (e.g. fuel) for releasingNO_(x) (e.g. stored NO_(x)) from the catalyst.

Generally, the engine management system is coupled to a sensor in theexhaust system, which monitors the status of the catalyst. Such a sensormay be disposed downstream of the catalyst. The sensor may monitor theNO_(x) composition of the exhaust gas at the outlet of the catalyst.

In general, the hydrocarbon is fuel, preferably diesel fuel.

Vehicle

Another aspect of the invention relates to a vehicle. The vehiclecomprises a diesel engine. The diesel engine is coupled to an exhaustsystem of the invention.

It is preferred that the diesel engine is configured or adapted to runon fuel, preferably diesel fuel, comprises ≤50 ppm of sulfur, morepreferably ≤15 ppm of sulfur, such as ≤10 ppm of sulfur, and even morepreferably ≤5 ppm of sulfur.

The vehicle may be a light-duty diesel vehicle (LDV), such as defined inUS or European legislation. A light-duty diesel vehicle typically has aweight of <2840 kg, more preferably a weight of <2610 kg.

In the US, a light-duty diesel vehicle (LDV) refers to a diesel vehiclehaving a gross weight of s 8,500 pounds (US lbs). In Europe, the termlight-duty diesel vehicle (LDV) refers to (i) passenger vehiclescomprising no more than eight seats in addition to the driver's seat andhaving a maximum mass not exceeding 5 tonnes, and (ii) vehicles for thecarriage of goods having a maximum mass not exceeding 12 tonnes.

Alternatively, the vehicle may be a heavy-duty diesel vehicle (HDV),such as a diesel vehicle having a gross weight of >8,500 pounds (USlbs), as defined in US legislation.

Definitions

The expression “bismuth (Bi), antimony (Sb) or an oxide thereof”includes “bismuth (Bi), or an oxide thereof or antimony (Sb) or an oxidethereof”.

The term “region” as used herein refers to an area on a substrate,typically obtained by drying and/or calcining a washcoat. A “region”can, for example, be disposed or supported on a substrate as a “layer”or a “zone”. The area or arrangement on a substrate is generallycontrolled during the process of applying the washcoat to the substrate.The “region” typically has distinct boundaries or edges (i.e. it ispossible to distinguish one region from another region usingconventional analytical techniques).

Typically, the “region” has a substantially uniform length. Thereference to a “substantially uniform length” in this context refers toa length that does not deviate (e.g. the difference between the maximumand minimum length) by more than 10%, preferably does not deviate bymore than 5%, more preferably does not deviate by more than 1%, from itsmean value.

It is preferable that each “region” has a substantially uniformcomposition (i.e. there is no substantial difference in the compositionof the washcoat when comparing one part of the region with another partof that region). Substantially uniform composition in this contextrefers to a material (e.g. region) where the difference in compositionwhen comparing one part of the region with another part of the region is5% or less, usually 2.5% or less, and most commonly 1% or less.

The term “zone” as used herein refers to a region having a length thatis less than the total length of the substrate, such as ≤75% of thetotal length of the substrate. A “zone” typically has a length (i.e. asubstantially uniform length) of at least 5% (e.g. ≥5%) of the totallength of the substrate.

The total length of a substrate is the distance between its inlet endand its outlet end (e.g. the opposing ends of the substrate).

Any reference to a “zone disposed at an inlet end of the substrate” usedherein refers to a zone disposed or supported on a substrate where thezone is nearer to an inlet end of the substrate than the zone is to anoutlet end of the substrate. Thus, the midpoint of the zone (i.e. athalf its length) is nearer to the inlet end of the substrate than themidpoint is to the outlet end of the substrate. Similarly, any referenceto a “zone disposed at an outlet end of the substrate” used hereinrefers to a zone disposed or supported on a substrate where the zone isnearer to an outlet end of the substrate than the zone is to an inletend of the substrate. Thus, the midpoint of the zone (i.e. at half itslength) is nearer to the outlet end of the substrate than the midpointis to the inlet end of the substrate.

When the substrate is a wall-flow filter, then generally any referenceto a “zone disposed at an inlet end of the substrate” refers to a zonedisposed or supported on the substrate that is:

-   (a) nearer to an inlet end (e.g. open end) of an inlet channel of    the substrate than the zone is to a closed end (e.g. blocked or    plugged end) of the inlet channel, and/or-   (b) nearer to a closed end (e.g. blocked or plugged end) of an    outlet channel of the substrate than the zone is to an outlet end    (e.g. open end) of the outlet channel.

Thus, the midpoint of the zone (i.e. at half its length) is (a) nearerto an inlet end of an inlet channel of the substrate than the midpointis to the closed end of the inlet channel, and/or (b) nearer to a closedend of an outlet channel of the substrate than the midpoint is to anoutlet end of the outlet channel.

Similarly, any reference to a “zone disposed at an outlet end of thesubstrate” when the substrate is a wall-flow filter refers to a zonedisposed or supported on the substrate that is:

-   (a) nearer to an outlet end (e.g. an open end) of an outlet channel    of the substrate than the zone is to a closed end (e.g. blocked or    plugged) of the outlet channel, and/or-   (b) nearer to a closed end (e.g. blocked or plugged end) of an inlet    channel of the substrate than it is to an inlet end (e.g. an open    end) of the inlet channel.

Thus, the midpoint of the zone (i.e. at half its length) is (a) nearerto an outlet end of an outlet channel of the substrate than the midpointis to the closed end of the outlet channel, and/or (b) nearer to aclosed end of an inlet channel of the substrate than the midpoint is toan inlet end of the inlet channel.

A zone may satisfy both (a) and (b) when the washcoat is present in thewall of the wall-flow filter (i.e. the zone is in-wall).

The term “adsorber” as used herein, particularly in the context of aNO_(x) adsorber, should not be construed as being limited to the storageor trapping of a chemical entity (e.g. NO_(x)) only by means ofadsorption. The term “adsorber” used herein is synonymous with“absorber”.

The term “mixed oxide” as used herein generally refers to a mixture ofoxides in a single phase, as is conventionally known in the art. Theterm “composite oxide” as used herein generally refers to a compositionof oxides having more than one phase, as is conventionally known in theart.

The acronym “PGM” as used herein refers to “platinum group metal”. Theterm “platinum group metal” generally refers to a metal selected fromthe group consisting of Ru, Rh, Pd, Os, Ir and Pt, preferably a metalselected from the group consisting of Ru, Rh, Pd, Ir and Pt. In general,the term “PGM” preferably refers to a metal selected from the groupconsisting of Rh, Pt and Pd.

The expression “consist essentially” as used herein limits the scope ofa feature to include the specified materials, and any other materials orsteps that do not materially affect the basic characteristics of thatfeature, such as for example minor impurities. The expression “consistessentially of” embraces the expression “consisting of”.

The expression “substantially free of” as used herein with reference toa material, typically in the context of the content of a washcoatregion, a washcoat layer or a washcoat zone, means that the material ina minor amount, such as ≤5% by weight, preferably ≤2% by weight, morepreferably ≤1% by weight. The expression “substantially free of”embraces the expression “does not comprise”.

The expression “about” as used herein with reference to an end point ofa numerical range includes the exact end point of the specifiednumerical range. Thus, for example, an expression defining a parameteras being up to “about 0.2” includes the parameter being up to andincluding 0.2.

Any reference to an amount of dopant, particularly a total amount,expressed as a % by weight as used herein refers to the weight of thesupport material or the refractory oxide thereof.

The term “selective catalytic reduction filter catalyst” as used hereinincludes a selective catalytic reduction formulation that has beencoated onto a diesel particulate filter (SCR-DPF), which is known in theart.

EXAMPLES

The invention will now be illustrated by the following non-limitingexamples.

Example 1

Pd nitrate was added to slurry of small pore zeolite with the AEIstructure and was stirred. Alumina binder was added then the slurry wasapplied to a cordierite flow through monolith having 400 cells persquare inch structure using established coating techniques. The coatingwas dried and calcined at 500° C. A coating containing a Pd-exchangedzeolite was obtained. The Pd loading of this coating was 80 g ft⁻³.

A second slurry was prepared by milling silica-alumina to a d90<20micron and adding a solution of bismuth nitrate. An appropriate amountof soluble Pt salt was added followed by beta zeolite such that theslurry comprised 23% zeolite and 77% alumina. The slurry was stirred tohomogenise then applied to the inlet channels of the cordierite flowthrough monolith. The coating was dried at 100° C.

A third slurry was prepared by milling manganese oxide-alumina to ad90<20 micron. An appropriate amount of soluble Pt salt was added andthe mixture stirred to homogenise. The slurry was applied to the outletchannels of the cordierite flow through monolith. The coating was driedat 100° C. and the catalyst calcined at 500° C. The Pt loading of thefinished catalyst was 67 g ft⁻³

Example 2 (Reference)

Pd nitrate was added to slurry of small pore zeolite with the AEIstructure and was stirred. Alumina binder was added then the slurry wasapplied to a cordierite flow through monolith having 400 cells persquare inch structure using established coating techniques. The coatingwas dried and calcined at 500° C. A coating containing a Pd-exchangedzeolite was obtained. The Pd loading of this coating was 80 g ft⁻³.

A second slurry was prepared by milling silica-alumina to a d90<20micron. An appropriate amount of soluble Pt salt was added followed bybeta zeolite such that the slurry comprised 23% zeolite and 77% alumina.The slurry was stirred to homogenise then applied to the inlet channelsof the cordierite flow through monolith. The coating was dried at 100°C.

A third slurry was prepared by milling manganese oxide-alumina to ad90<20 micron. An appropriate amount of soluble Pt salt was added andthe mixture stirred to homogenise. The slurry was applied to the outletchannels of the cordierite flow through monolith. The coating was driedat 100° C. and the catalyst calcined at 500° C. The Pt loading of thefinished catalyst was 67 g ft⁻³

Experimental Results

The catalysts of examples 1 and 2 were hydrothermally aged (with water)at 750° C. for 15 hours. The aged catalysts were testing by fitting to a2.0 litre bench mounted diesel engine. The engine ran simulated MVEG-Bcycles with exhaust gas emissions measured at both pre- andpost-catalyst positions. The CO and HC oxidation performance and NO_(x)storage properties over the MVEG-B cycle were evaluated. The results areshown in Table 1.

TABLE 1 Example Total CO Total HC conversion Cumulative NO_(x) No.conversion (%) (%) storage at 850 s (g) 1 64 75 0.85 2 52 70 0.7

The catalyst of example 1 shows higher CO and HC conversion efficiencyover the MVEG-B cycle than the catalyst of example 2. Example 1comprises bismuth at the inlet end of the catalyst. Example 1 also showshigher NO_(x) storage capacity at 850 seconds into the MVEG-B cycle thanexample 2.

Example 1 (according to the invention) shows improved CO and HCoxidation performance and improved NO_(x) storage properties thanexample 2.

Example 3

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by anappropriate amount of soluble Pt salt. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a Pt loading of 60 g ft⁻³and a Bi loading of 50 g ft⁻³, and a washcoat loading of 1.7 g in⁻³.

Example 4

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by appropriateamounts of soluble Pt and Pd salts. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C. andcalcined at 500° C. The finished catalyst has a total PGM loading of 60g ft⁻³ with a Pt:Pd weight ratio of 20:1, and a Bi loading of 50 g ft⁻³,and a washcoat loading of 1.7 g in⁻³.

Example 5

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by appropriateamounts of soluble Pt and Pd salts. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a total PGM loading of 60g ft⁻³ with a Pt:Pd weight ratio of 7:1, and a Bi loading of 50 g ft⁻³,and a washcoat loading of 1.7 g in⁻³.

Example 6

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by appropriateamounts of soluble Pt and Pd salts. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a total PGM loading of 60g ft⁻³ with a Pt:Pd weight ratio of 5:1, and a Bi loading of 50 g ft⁻³,and a washcoat loading of 1.7 g in⁻³.

Example 7 (Reference)

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. An appropriate amount of soluble Pt salt was added and theslurry was stirred to homogenise. The resulting washcoat was applied toa cordierite flow through monolith having 400 cells per square inchstructure using established coating techniques. The coating was dried at100° C., and calcined at 500° C. The finished catalyst has a Pt loadingof 60 g ft⁻³ and does not comprise Bi.

Example 8

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by anappropriate amount of soluble Pt salt. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a Pt loading of 60 g ft⁻³and a Bi loading of 50 g ft⁻³.

Example 9

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by anappropriate amount of soluble Pt salt. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a Pt loading of 60 g ft⁻³and a Bi loading of 100 g ft⁻³.

Example 10

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by anappropriate amount of soluble Pt salt. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a Pt loading of 60 g ft⁻³and a Bi loading of 150 g ft⁻³.

Example 11 (Reference)

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. An appropriate amount of soluble Pt salt was added. The slurrywas stirred to homogenise. The resulting washcoat was applied to acordierite flow through monolith having 400 cells per square inchstructure using established coating techniques. The coating was dried at100° C., and calcined at 500° C. The finished catalyst has a Pt loadingof 60 g ft⁻³ and a washcoat loading of 1.0 g in⁻³.

Example 12 (Reference)

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. An appropriate amount of soluble Pt salt was added. The slurrywas stirred to homogenise. The resulting washcoat was applied to acordierite flow through monolith having 400 cells per square inchstructure using established coating techniques. The coating was dried at100° C., and calcined at 500° C. The finished catalyst has a Pt loadingof 60 g ft⁻³ and a washcoat loading of 1.5 g in⁻³.

Example 13

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by anappropriate amount of soluble Pt salt. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a Pt loading of 60 g ft⁻³,a Bi loading of 50 g ft⁻³ and a washcoat loading of 1.0 g in⁻³. Theweight ratio of washcoat:Bi was approximately 35:1.

Example 14

Silica-alumina powder was slurried in water and milled to a d₉₀ <20micron. A solution of bismuth nitrate was added followed by anappropriate amount of soluble Pt salt. The slurry was stirred tohomogenise. The resulting washcoat was applied to a cordierite flowthrough monolith having 400 cells per square inch structure usingestablished coating techniques. The coating was dried at 100° C., andcalcined at 500° C. The finished catalyst has a Pt loading of 60 g ft⁻³,a Bi loading of 50 g ft⁻³ and a washcoat loading of 1.5 g in⁻³. Theweight ratio of washcoat:Bi weight was approximately 52:1.

Experimental Results

Core samples were taken from the catalysts of Examples 3 to 14. Thecores were hydrothermally aged at 800° C. for 16 hours using 10% water.

The catalytic activity for all cores was determined using a syntheticgas bench catalytic activity test (SCAT). The aged cores were tested ina simulated exhaust gas mixture shown in Table 2. In each case thebalance is nitrogen.

TABLE 2 CO 1500 ppm  HC (as C₁) 430 ppm NO 100 ppm CO₂ 4% H₂O 4% O₂ 14% Space velocity 55000/hour

The oxidation activity for CO and HC is determined by the light offtemperature whereby 50% conversion is achieved (T50). SCAT results areshown in Tables 3 to 5.

TABLE 3 Example No. T50 CO (° C.) T50 HC (° C.) 3 137 176 4 141 177 5164 191 6 168 190

The results shown in Table 3 show the CO and HC light off temperaturesfor the catalysts of Examples 3 to 6.

Examples 3 and 4 show a low light off temperature for both CO and HC.Examples 3 and 4 have Pt:Pd weight ratios of 1:0 and 20:1 respectively.

Examples 5 and 6 have higher light off temperatures for CO and HC.Examples 5 and 6 have Pt:Pd weight ratios of 7:1 and 5:1 respectively.

TABLE 4 Example No. T50 CO (° C.) T50 HC (° C.)  7 (Reference) 187 192 8 147 196  9 143 222 10 194 369

The results shown in Table 4 show the CO and HC light off temperaturesfor the catalysts of Examples 7 to 10.

Example 8 has a low light off temperature for both CO and HC. Example 8comprises Bi at 50 g ft⁻³ loading.

Example 9 has a low light off temperature for CO, but a relatively highlight off temperature for HC. Example 9 comprises a Bi loading of 100 gft⁻³.

Example 10 comprises Bi at the highest loading of 150 g ft⁻³ and has thehighest light off temperatures for CO and HC.

TABLE 5 Example No. T50 CO (° C.) T50 HC (° C.) 11 (Reference) 182 18812 (Reference) 176 183 13 145 214 14 145 190

The results shown in Table 5 show the CO and HC light off temperaturesfor the catalysts of Examples 11 to 14. All catalysts have the same Ptloading and same Bi loading where applicable.

Examples 13 and 14 have a low light off temperature for CO compared withExamples 11 and 12. Examples 13 and 14 comprise Bi. Example 14 also hasa low light off temperature for HC. Example 14 has a washcoat:Bi weightratio of 52:1. Example 13 which has a higher light off temperature forHC has a washcoat:Bi weight ratio of 35:1.

The results for Examples 3 to 6 show that the inclusion of Bi with ahigher weight ratio of Pt:Pd provides a lower CO and HC light offtemperature. Examples 8 and 9 show that lower loadings of Bi arepreferred to maintain both good CO and good HC oxidation activity.Examples 11 to 14 show that a high weight ratio of washcoat:Bi providesboth good CO and good HC oxidation activity.

Example 15

Bismuth nitrate was dissolved in 2M nitric acid and impregnated onto asilica-alumina powder (5% silica by mass) using an incipient wetnessmethod. The material was dried at 105° C. then calcined at 500° C. Thecalcined powder was impregnated with a platinum nitrate solution by anincipient wetness method. The material was dried at 105° C. thencalcined at 500° C. The final catalyst powder had a Pt loading of 1.7 wt% and a Bi loading of 4 wt %.

Example 16

Bismuth nitrate was dissolved in 2M nitric acid and impregnated onto analumina powder using an incipient wetness method. The material was driedat 105° C. then calcined at 500° C. The calcined powder was impregnatedwith platinum nitrate solution by an incipient wetness method. Thematerial was dried at 105° C. then calcined at 500° C. The finalcatalyst powder had a Pt loading of 1.7 wt % and a Bi loading of 4 wt %.

Experimental Results

The catalysts of Examples 15 and 16 were hydrothermally aged in an ovenat 750° C. for 15 hours using 10% water. The catalytic activity wasdetermined using a synthetic gas bench catalytic activity test (SCAT).0.4 g of aged catalyst powder in the size fraction of 255 to 350 micronswas tested in a simulated exhaust gas mixture shown in Table 6. In eachcase the balance is nitrogen. The oxidation activities for CO and HC aredetermined by the light off temperature whereby 50% conversion isachieved (T50). SCAT results are shown in Table 7.

TABLE 6 CO 1500 ppm  HC (as C₁) 480 ppm NO 150 ppm CO₂ 5% H₂O 5% O₂ 14% Gas hourly space velocity 28000 ml/hr/ml

TABLE 7 Example No. T50 CO aged condition (° C.) T50 HC aged condition(° C.) 1 121 163 2 138 186

Table 7 shows the CO and HC T50 light off temperatures for Examples 15and 16. Example 15 has a lower light off temperature than Example 16.Example 15 comprises Pt/Bi and a silica-alumina refractory oxide supportmaterial. Example 16 comprises Pt/Bi and an alumina refractory oxidesupport material.

Example 17

Antimony was impregnated onto a silica-alumina powder (5% silica bymass) using a soluble antimony salt (an antimony tartrate solution) viaan incipient wetness method. The antimony tartrate solution was preparedby refluxing antimony oxide in an excess of tartaric acid.

The Sb-impregnated silica-alumina material was dried at 105° C. thencalcined at 500° C. The calcined powder was then impregnated withplatinum nitrate solution by an incipient wetness method. The materialwas dried at 105° C. then calcined at 500° C. The final catalyst powderhad a Pt loading of 1.7 wt % and a Sb loading of 4 wt %.

Example 18

Antimony was impregnated onto a silica-alumina powder (5% silica bymass) using an antimony tartrate solution via an incipient wetnessmethod. The material was dried at 105° C. then calcined at 500° C. Thecalcined powder was impregnated with platinum nitrate solution by anincipient wetness method. The material was dried at 105° C. thencalcined at 500° C. The final catalyst powder had a Pt loading of 1.7 wt% and a Sb loading of 2 wt %.

Example 19

Bismuth nitrate was dissolved in 2M nitric acid and impregnated onto analumina powder using an incipient wetness method. The material was driedat 105° C. then calcined at 500° C. The calcined powder was impregnatedwith platinum nitrate solution by an incipient wetness method. Thematerial was dried at 105° C. then calcined at 500° C. The finalcatalyst powder had a Pt loading of 1.7 wt % and a Bi loading of 4 wt %.

Example 20

Platinum was impregnated onto a silica-alumina powder (5% silica bymass) using a platinum nitrate solution via an incipient wetness method.The material was dried at 105° C. then calcined at 500° C. The finalpowder had a Pt loading of 1.7 wt %.

Experimental Results

The catalytic activity of the catalysts of Examples 17, 19 and 20 in afresh (i.e. unaged) state was determined using a synthetic gas benchcatalytic activity test (SCAT). 0.4 g of catalyst powder in the sizefraction of 255 to 350 microns was tested in a simulated exhaust gasmixture having a composition as shown in Table 6. In each case thebalance is nitrogen. The oxidation activities for CO and HC aredetermined by the light off temperature whereby 50% conversion isachieved (T50). The SCAT results are shown in Table 8.

TABLE 8 NO Oxidation T50 CO fresh T50 HC at 250° C. (%) Example No.condition (° C.) fresh condition (° C.) fresh condition 17 115 147 75 19113 167 26 20 138 153 84

Table 8 shows the CO and HC T50 light off temperatures as well as NOoxidation at 250° C. for Examples 17, 19 and 20 in the fresh condition.Example 17 has a lower light off temperature than Example 20. Example 17comprises Pt/Sb and a silica-alumina refractory oxide support material.Example 20 comprises Pt and a silica-alumina refractory oxide supportmaterial. Example 17 has a lower HC light off than Example 19 and betterNO oxidation activity. Example 19 comprises Pt/Bi and a silica-aluminarefractory oxide support material.

The catalysts of Examples 17 to 20 were hydrothermally aged in an ovenat 750° C. for 15 hours using 10% water. Their catalytic activity wasdetermined using a SCAT as described above using 0.4 g of aged catalystpowder in the size fraction of 255 to 350 microns and the simulatedexhaust gas mixture shown in Table 6 (the balance is nitrogen). The SCATresults are shown in Table 9.

TABLE 9 NO Oxidation T50 CO aged T50 HC at 250° C. (%) Example No.condition (° C.) aged condition (° C.) aged condition 17 162 179 82 18167 178 82 19 130 162 73 20 184 187 84

Table 9 shows the CO and HC T50 light off temperatures as well as NOoxidation at 250° C. for Examples 17 to 20 in the aged condition.Example 17 has a lower light off temperature than Example 20.

For the avoidance of any doubt, the entire content of any and alldocuments cited herein is incorporated by reference into the presentapplication.

1. An oxidation catalyst for treating an exhaust gas produced by adiesel engine comprising a catalytic region and a substrate, wherein thecatalytic region comprises a catalytic material comprising: bismuth(Bi), antimony (Sb) or an oxide thereof; a platinum group metal (PGM)selected from the group consisting of (i) platinum (Pt), (ii) palladium(Pd) and (iii) platinum (Pt) and palladium (Pd); and a support material,which is a refractory oxide; wherein the platinum group metal (PGM) issupported on the support material; and wherein the bismuth (Bi),antimony (Sb) or an oxide thereof is supported on the support material.2. An oxidation catalyst according to claim 1, wherein the refractoryoxide is a particulate refractory oxide, and the bismuth, antimony or anoxide thereof is dispersed over a surface of the particulate refractoryoxide.
 3. An oxidation catalyst according to claim 1, wherein thecatalytic material comprises bismuth (Bi) or an oxide thereof.
 4. Anoxidation catalyst according to claim 3, wherein the refractory oxide isa particulate refractory oxide having a bulk particulate structure, andthe bismuth or an oxide thereof is contained within the bulk particulatestructure of the refractory oxide.
 5. An oxidation catalyst according toclaim 3, wherein refractory oxide is impregnated with bismuth or anoxide thereof.
 6. An oxidation catalyst according to claim 1, whereinthe catalytic region has a total loading of bismuth or antimony of 1 to200 g ft⁻³.
 7. An oxidation catalyst according to claim 3, wherein therefractory oxide further comprises tin (Sn) or an oxide thereof.
 8. Anoxidation catalyst according to claim 1, wherein the catalytic materialcomprises bismuth or antimony in an amount of 0.1 to 15.0% by weight. 9.An oxidation catalyst according to claim 1, wherein the catalytic regioncomprises bismuth or antimony in an amount of 1.0 to 2.5% by weight. 10.An oxidation catalyst according to claim 1, wherein the refractory oxidecomprises alumina, silica or a mixed or composite oxide of silica andalumina.
 11. An oxidation catalyst according to claim 1, wherein therefractory oxide comprises alumina doped with silica.
 12. An oxidationcatalyst according to claim 1, wherein the platinum group metal (PGM) isplatinum (Pt).
 13. An oxidation catalyst according to claim 1, whereinthe platinum group metal (PGM) is palladium (Pd).
 14. An oxidationcatalyst according to claim 1, wherein the platinum group metal (PGM) isplatinum (Pt) and palladium (Pd).
 15. An oxidation catalyst according toclaim 1, wherein the catalytic material comprises a ratio by weight ofthe platinum group metal (PGM) to bismuth (Bi) or antimony (Sb) of 10:1to 1:10.
 16. An oxidation catalyst according to claim 1, wherein thesubstrate is a flow-through monolith or a filtering monolith.
 17. Anexhaust system for treating an exhaust gas produced by a diesel engine,wherein the exhaust system comprises the oxidation catalyst of claim 1and optionally an emissions control device.
 18. A vehicle comprising adiesel engine and an exhaust system according to claim 17.